Stage 4 means the cancer has spread outside the bladder. It's the metastasis part that can involve other organs (lungs, bones, brain, etc.).
The reason there are not tons of replies when talking about that stage is that most of us here never got to that stage (and we're all hoping we never do). That's really the main reason. As for myself, I don't know a whole lot about the details when things get to that stage because I haven't studied it. Now, if I wind up having a recurrence and metastatic disease, you can bet I will be studying the hell out of it.
Mets is bad news. Mets is always bad news. Is mets always the end? No. Chemo can and does help and some people are cured but the numbers/statistics aren't great for long term survival. But even if the probably of 10 year survival was 10%, if you are one of the people in the 10% group, you are 100% alive. So, from a probability standpoint things don't look great but that doesn't mean there is any certainty either way. I just made up the 90/10 number for the purpose of an example. I don't know what the statistics are because they probably don't really matter. It's either it works (the chemo) or it doesn't.
Hoping for the best for your husband and for you!
Mike