Well, for someone who claims to have "no specialist knowledge of the conflict", you sure are making a number of predictions, that may or may be not come to pass :)

will probably, ultimately, cost Putin his job.

Possibly. Then again, one can think a lot of scenarios where Putin does remain in place. Russia will be in a much worse state though...

he will have to settle for some territorial gains around Donbass and Mariupol

Depends on how far Ukrainian counter-attacks go; many things could still happen and I'm expecting the unexpected. Who would have thought, just a month ago when the Russian invasion had just started, that we would be in the present situation? (The most likely scenario was Russia quickly squashing Ukrainian forces)

Europe will also reduce its dependency on Russian oil and exports and take a much more hardline approach to all Russian initiatives

Hopefully, the mere realization of "it could happen to us" will jolt the Europeans (not only the EU) to keep building a more resilient society, especially vis a vis the imported fossil fuels. But there is also a strong temptation to resume "business as usual", as soon as possible, with maybe, most Russian gas replaced with US liquefied shale gas... Complacency is strong among our elites.

as the costs for the EU and its members have also been considerable.

Not yet: the true costs of cutting Russian energy imports off and having to deal with our economy's dependence on imported fossil fuels has just barely started to bite. Expelling Russian spies/diplomats is painless. Re-calibration will be a long and difficult process.

That's probably the pessimistic me reacting to the optimistic you, with a pinch of Gallic skepticism :)

In any case, this is a stronger case than ever to re-enforce the ties between EU countries, and even outside of the EU.