There are always options. Opera could have doubled-down on Presto; putting more people on the core team, and focussing efforts to keep up with, and surpass, WebKit/Gecko. After all, that's basically the option that Mozilla took, which has resulted in Firefox Quantum. Would that have worked? It's hard to say. I would guess not, but I'm not sure the alternative really did either. Maybe Opera was already too far down the web-compat death spiral to engineer a way out. I don't know of a long-term bet like Rust that could have come good at the right time.
Certainly the top-level culture of the organisations was different; Opera's leadership were very concerned with maintaining/maximising the value of their shares, whereas Mozilla is more clearly driven by ideological goals around the success of the open web. Opera also had a (historically well justified) belief that they could do more with fewer engineers than other compaines. That seemed to work up to a point, but once the difference in resources became too great it was hard to change the approach.
Certainly one lesson is that it's hard, maybe impossible, to be a niche browser with a unique rendering engine. That is arguably a failing of the web, but nevertheless it's a strong indication that arguments that e.g. Mozilla should aim Firefox at small ideologically-driven markets are dangerous. One interpretation of the Opera history is that they were too focussed for too long on the subset of users who wanted a browser with lots of features and configuration possibilities. A product that suits those people might be actively offputting to other users, so inhibiting marketshare growth when faced with competition targetting simplicity and sane defaults.
