It is possible to pack the PC and that it would arrive safely but there are precautions to take that will help but not guarantee its safety due to rough handling. Turns out I have successfully taken an entire PC between North and South America twice and only had a slight cosmetic damage the last time.
Ideally, I would pack the PC into the box that the case was sold in which usually has styrofoam exactly the right shape and designed to ship the case. Not all airlines accept boxes as luggage or you may not have the box and neither did I, so this is how it worked for me:
- Wrap the entire computer in a yoga mat or towels and tape that all around so that it does not move. Not doing so once made the towels moved and expose a corner of the case.
- Place the wrapped computer case inside a hard-shell suitcase. This meant shopping for a suitcase as I also had a fairly large case and only found one 31" hard-shell where it fit with all the padding.
- Remove rotating HDD from the PC and place in your carry-on. Not wanting to deal with installing a new CPU fan unnecessarily, I left it in the PC but took a spare one in my carry-on just in case.
- Fill open spaces in the PC case with foam blocks. This was to make the case more rigid so that any give in the suitcase would not be delivered to the PC only when stacked among other luggage.
- When handing the suitcase to baggage-drop, told them it was fragile and they added a warning label. This had two side-effects: One is that someone carried the suitcase to the rolling cart rather than putting it on the luggage belt. The other is that they made me sign a waiver saying they were not responsible for damage!
To make things easier should anything happened, I also removed the SSDs and placed them in my carry-on. That way, at least it was possible to get back my system up and running if the PC did not make it.
It is hard to imagine selling and buying again is worth it if your system is reasonably new unless you are taking it to a market where electronics are much cheaper than where you bought it.
Honestly, I didn't think of taking it appart and leaving the case but that sounds like a good idea. Packing each part will be easier and take less space. If you don't have unusual requirements for a case, that could work well. Again, pack everything carefully as above.
Lastly, there is no guarantee that anything won't happen, so prepare a contingency plan. Make sure to carry backups separately or have them cloud-based. Purchase extra insurance if your PC is expensive. Luggage does get lost too. With pricey equipment, it is even more likely in some places.