I wouldn't be so sure. Symbiotes are the main topic of this season, but their invasion is not a topic in ALL episodes. I mean, sure, we had the warning of Star-Lord on the previous episode, but most of it didn't have symbiotes. After the symbiote's invasion, there can be other topic related with them. You know, like in "Ultimate Spider-Man: Web Warriors". After the Venomized Asgardian invasion of Loki and Doc Ock, they had to deal with remains of symbiotes several times. One of them was Flash becoming Agent Venom. The same happened after the "Carnage Island" arc, with Mary Jane becoming Spider-Woman. The last two episodes could be about something similar, and I bet one of them would be Norman Osborn as the red Goblin.Well, the whole season is about the Symbiote Invasion so I'd water it'll probably carry on until the end.