I believe that you get it back once you have shown sufficient in game behavior that is reformed. I don't think Riot has a specific time or number of games that is hard set as I am pretty sure it is determined by what your offense was. If I recall correctly, Riot has never publicly stated what the exact reform duration is.
If you abandon your account, it will take a lot of time to get all of your runes, rune pages, and the champs back with IP unless you spend real money and purchase RP but you still need runes with IP so regardless it'll take time.
Remember, hextech loot isn't gone forever. It's just gone as a hard reminder that you could have gotten chests and keys but are not because you treated your fellow teammates poorly. Once you are truly good and cooperative with your teammates again, hextech will come back for you.