Amatara

I think it's a small miracle that he ever went back to Londo after what he'd been put through for the purpose of revenge on Refa; and the fact that he did is a sign of strength rather than of weakness, of giving in.

Agreed. I don't know if I would have been able to forgive Londo either, but it's typically Vir to be able to forgive. I personally think he was able to see the good in Londo that was buried so deep, nobody else could see it -including, maybe, Londo himself. I'm sure it wasn't easy.

what did you feel when reading the ending? Do you think it's fitting?

I think it's very fitting because that, too, is very Vir -to be able to hope for a better future.
As for what the future hold for them, it depends on how far you look. I can understand what the commenter said because a few years from now will be a dark time for the Centauri. But in the end, I think they will make it all right. Londo will begin the process by dying and Vir will continue it once he becomes emperor, making the Centauri a member of the Alliance again, as seen in Sleeping in Light. (nice icon, btw)
It will take years, and these will not be good years, but they will make it all right.
Well, that's how I see it anyway.