[Update]: The Last Chance event has now arrived, so if there's any skin that you'd like to grab, this would be the time to do so.
Once Overwatch 2 arrives this October, all of your in-game credits from the original will be transferred over. However, while you will still be able to use these credits to purchase some of the fancier cosmetics, you'll most likely have to wait for their associated events to cycle back in order to unlock them, which in the case of the Summer Games skins could be an entire year!
So if there is any sort of skin, voice line or animation you're itching to grab, you'll be happy to hear that Blizzard will be launching the Last Chance event this September 13th. As the name might imply, this event will open up the vaults and allow you to purchase any time-gated cosmetic from any of the seasonal updates.
If you currently don't have enough in-game currency to snag your favorites, worry not as you have a decent bit of time on your hands. I say this because the Last Chance event will only be going away on October 2nd, a mere few days before Overwatch 2 arrives.
On a slightly unrelated note, you might also want to know that new Overwatch 2 heroes will need to be unlocked through the free Battle Pass. The exact details are still unavailable since most of this information comes from an accidental leak, but what I can tell you is that the next hero to be revealed will highly likely be the fox girl support Kiriko.
Once the full announcement goes live, probably alongside the Last Chance event, I'll make sure to let you know. Enjoy!