Well you’ll lose any gear you have equipped and in the inventory on your character. But everything in the vault for that character will still be there. Bungie said that all characters created before WQ will get all the pre-raid Void 3.0 abilities from the start. Which would imply if you make a new character after the WQ release you may need to quest to obtain those. You will also need to reacquire Stasis and it’s Aspects for that class. The character will have to go through the new light quest, and won’t be seen as having completed the ShadowKeep or Beyond Light campaigns. So there will be some activities you won’t have access to until you reach certain points in those campaigns. I think that’s it. I believe collections and triumphs are all account based, so they won’t go anywhere.