The trick is probably to not leave Europe in the first place.
I could have stayed in Europe, and spent another 5 years not moving on the seniority list. In fact if I had of stayed id have moved backwards on it. All while struggling to pay for my families monthly shopping bill, watching airline stagnation completely ruin my career, instead of eating out twice a week in 5 star resorts, drinking beer on the beach, and driving around in my ridiculously uneconomical american muscle car. If an airline could offer me all that back home then of course I wouldn't have ever left, but it doesn't exist! You are confusing 'frustration, compromise, despair' with 'reality'
you won't catch up on lost seniority and commensurate income.
Thats a huge sweeping statement. I personally left Europe as a turboprop FO, I could return now as a jet DEC if I wanted. That would mean I in fact leapfrog most of my 'senior' ex-colleagues and I have earned & more importantly saved far more than them too.