Nothing much.

I'd have to find a replacement for Google Maps and YouTube, but I guess I could just create a new account for that.

I use ProtonMail and iCloud for email and calendar respectively. DockDuckGo for search, Firefox for rendering web content.

I backup everything to multiple locations/services, so I'm not too worried about loosing access to things in general.

Guess the most annoying thing to loose access to would be Facebook as I have a few contacts on there that I wouldn't immediately know how else to contact, but I'm sure I'd find a way if I really had to.