With the i7-2500K, the system should last several more years over the Ivy Bridge & Haswell (3rd & 4th gen 'i' series), as Intel was still soldering the IHS (the part were we apply thermal paste) in place, which allows for better cooling. AMD kept this practice.
I say this because most all Intel quad core CPU's after Sandy Bridge now are bonded together with cheap thermal paste & glue, although Intel stated that they used a 'better' solution on the Devil's Canyon CPU's (the i5-4690K & i7-4790K, of which I have both). Only a delid & replace the thermal solution with liquid metal can drop temps to where a stock Sandy Bridge runs at idle & under load, or use some form of liquid cooling, which I won't use due to safety.
Bottom line, a i7-2500K can be stored for years & run just like when placed back in use, with the newer CPU's, one has to be concerned with the thermal paste drying out, it's not a matter of if, rather when. If removed & stored for a few years, the paste may break down & has to be replaced ASAP if temps are high at idle. Otherwise, there'll be thermal runaway & it's a one way trip. the CPU becomes shot.
This is why many hangs onto their Sandy Bridge CPU's, the i7-2500K (if new) now sells for more than released, and even used ones retains high value on eBay, as well as MB's for the series. Many who has upgraded to a i7-6700K/7700K has ended up regretting selling their i7-2500K CPU's, to this date, maybe a 10% performance increase, less if their 2500K were overclocked.
I now have an even mixture of Intel & AMD builds, and when it comes time to build a new main rig (around 2020), will go AMD. Even if there's a slight single core drop in performance, doesn't matter to me, because am not a gamer, just want a nice, powerful system. Today's AMD CPU's would give me just that, and I expect things to improve even more by the time I'm ready to 'catch up with the Jones's'.
MDD1963 gave excellent advice above, having an external drive for disk imaging & storage of important data is critical not only for the sake of recovery, now add security to the list to prevent having to pay a ransom for your files. I use Macrium Reflect to create weekly images of my most important builds, and never store important documents on the 'C' drive, will place on an internal Data drive instead & then transfer to one or more externals. Macrium (free edition) also has an option to add an entry to the bootloader for imaging disks, this makes for fast backups, although keep the latest WinPE ISO on an external if I need to clone a drive, or an infection hits the OS. I'd then securely erase the drive before restoring the last image, using Parted Magic & the Full erase (not the offered 'enhanced' option), takes under a minute for most SSD's except for very large models. If HDD, will first use a bootable partition tool to reset the MBR, then use DBAN to wipe the HDD with the 'autonuke' option, which is a DOD certified 3 pass wipe and a last scattering random data. Not even the FBI, CIA or any other agency recover any data, yet for most, the important part is ensuring all traces of Malware/Ransomware are securely deleted.
So it's not only important to image the OS drive, also any Data ones. And one doesn't have to purchase low quality & useless if the connector becomes broken retail packaged externals. I use USB 3.0 & eSATA enclosures and/or a docking station (have 4 enclosures & two docking stations) & several extra HDD's laying around packaged well, or if needed, will purchase a 'bare drive' on promo. Most of my backup drives are 1TB retired models from the SATA-2 era (one WD Caviar Black, an RE4 & two Samsung HD103SJ), in excellent condition & I perform tests on all at least once per year, the extended one. If needed, I'd not have issue with placing either back in active service as Data drives, are likely better than most new ones of today. I use smaller 160-250GB drives (a couple SATA-1) for imaging my notebooks with a docking station. The only useless drive is a dead one in my place.
As far as an SSD goes, a 250-256GB model is the 'sweet spot', and if the Documents, Downloads, Pictures/Videos & other items are stored on the internal Data drive, the SSD will always have plenty of free space. I have a few secondary systems running some of my original 120-128GB SSD's, combined with a 500GB to 1TB HDD & still am fine, even after leaving 10GB of unformatted space at the end of the SSD (recommended). This keeps the SSD fast & room for the controllers to do it's job, and if needed, can replace a bad block with one in the unallocated space (better known as over provisioning). Most all SSD OEM's recommends this practice & some has the software to manage the space, although 10% of a 500GB or larger model is overkill, 25GB of free space is plenty, up to 1TB.
BTW, I also have one of the IcyDock 5.25" dual 3.5"/2.5" removable drive adapter bays that MDD1963 was speaking of, great for having two SSD's, or a SSD & 2.5" HDD and low cost. I used the opening in front to also install a TechRepublic USB 3.0 two port hub (1st link below), so made the most out of the adapter & backup speeds are faster than the ports on the MB's panel.
Here's the IcyDock 5.25" dual 3.5"/2.5" removable drive adapter bay.
Newegg also has it with free shipping available, although I prefer B&H when an item is needed fast.
You'll always have room for upgrades in your PC, it's a matter of your priorities & budget that'll make the right decisions & I'll repeat for one last time, your i7-2500K is still relevant in 2017. There are many who wouldn't take what they paid for the build when these were popular ones, the proof is all over these various Tech Forums, especially the ones associated with overclocking.