Lifetime is implied to be the lifetime of the company as is the case with LITERALLY EVERYTHING.
From an economic view: In this case as soon as you hit 13 months without filen going bankrupt you are literally free compared to the 200GB plan with Google Drive which you would still be stuck paying $4 CAD/month for 200GB long after the lifetime plan has paid for itself (assuming they don't increase monthly rates as time goes on, which they always do).
Go ahead and pay monthly if you want but you'll be in exactly the same position if a company goes under, except you would have paid a hell of a lot more than 35 Euro by that point.
This is literally client-side encryption using fully open source programs... If you "do not trust it to be e2e", verify the code yourself. Doing your own encryption on top would be redundant.