The last Spiderman movie proved you don't need Tony Stark in it. It is the highest grossing Spiderman movie to date.
Really Ed? Far From Home was completely devoid of Tony Stark?
It was devoid of Robert Downey Jr. The plot may have revolved around Peter being the heir apparent to Tony, but we didn't even get a RDJ cameo unless you count a picture of him on the school new broadcast. It is essentially like Luke Skywalker in TFA. The opening crawl leads one to believe that the plot of the movie would be around finding Luke, only to find out we get a half a minute at best of him on screen. By comparison, this movie had less actual Tony Stark in it, but did just fine.
Can the next one stand on its own? Who knows. Spiderman still had Happy Hogan, Nick Fury, and Maria Hill in it. It will be pretty jarring for the next one to not have any MCU characters, especially if they can't even be mentioned.
Personally, I think the deal isn't truly dead yet. If they put out a Venom 2 first and that isn't successful, I think things will get renegotiated. I foresee Sony having problems with a Spiderman 3 script. So far, they haven't recycled villains, with the exception of introducing Harry as the Green Goblin at the very end of the second Garfield movie. Not sure who you would choose at this point if you wanted to go with an unused villain.