If we use his contemporaries as precedents:
Federer at 35-38
4 Finals, 3 Wins (Nadal, Cilic, Cilic)
2 Semifinals, routine losses to Nadal and Novak (injured)
Career Over after 38 and a half
Nadal 35-37
2 Finals, 2 Wins (Ruud, Medvedev)
2 Semifinals, tough loss to Novak, injured walkover to Kyrgios
Career seemingly over at just over 36
I mean....Novak could win 3 more Slams or make 4 more Semis at least or he could be rocked at this year's USO and never contend again......har, har but true. I guess with Covid and the Sandgren match after a twilight bonanza for Fed it could mean Novak has 3 more years with his stretching and taking a lighter schedule. I'd be inclined to go with that over his career being done now. I think the field is largely irrelevant. Sure you could say Sinner, Alcaraz or Rune knocks him off but no definitive consistency and he's shown he can well compete and beat all of those guys.
Anywho I voted 2025 veering more the Fed route as he's a contender on every surface but perhaps like Fed he starts skipping some Slams like the French it will obviously depend on him thinking about his chances against the field. Hard to imagine he won't be at least a Top 4 contender for AO/WMB at least 2 more editions as always barring injury.