The greatest fear of the EU in giving the UK any sort of a "deal" upon exit was that other states would begin to see leaving as a feasible option.
Regardless of whether you believe Brexit will be negative, positive or neutral, it is now possible to leave - and with a deal.
I think that Italy and Greece will see a resurgence of exit sentiments - particularly after what happened to Italy during the pandemic. Possibly also Scotland - which the EU may allow to join now simply to make other leavers think carefully about their regions e.g. Catalonia.
Who do you think will be next to hold a referendum? Or do you think the EU will now pursue closer legal ties than ever e.g. the posited one Euro army?