From purely a financial perspective you'd be betting the USD
over the Euro. Both currencies are in deep !!!! and set to get
deeper - but my money would be on the Euro sinking first. A
tough call but no one can be 100% accurate (VN I think still
pays in USD) If it was yuan or swiss francs it's be a different
story.
Careerwise it'd be better to stay put where you are unless LH
goes tits up, and just visit Nam during time off. Never worked
for VN itself but I do know it aint all beer and skittles.