We'll just have to wait and see, but i'm sure that 2020's will be a century that Stena Line will begin withdrawals of the 80's vessels.
But i can tell despite everything Stena Europe is in a decent condition though in my opinion, but we have to realise that age is catching up with her as well, and despite Stena Vision for example being 6 years newer you can clearly see that it has some wear and tear. The so called Comfort class cabins could do with a big refit, but only thing that has been done is to paint the walls in the bathrooms on them, and that's it, they've been like that since they left the Germany route in 2010.
The reason that Stena Danica may be in an excellent condition is because it stays in Gothenburg during the day some days, according to a friend who works onboard he tells me that it requires quite a lot of maintenance in the latest days, he's even had some questions from some Gothenburgers about when the Göteborg-Frederikshavn will have a new ship as the Danica has been there for all it's eternity...