ARGH! That's a bad one!
But there are some extreme measures that can get you in if the situation is right and it may not cause any big, big damage if you are replacing the latch and handle any way!
Looking at this page of the parts catalog for a view of what's inside and an idea.
https://www.winnebago.com/Files/File...04/4wfd30b.pdf
Click this snip for best view or go direct to get parts and the whole story?
Study carefully as this idea can take some grit to do it without seeing really where you are going! Open windows are nice but they are also very expensive and terrible to replace, so I favor the door.
Is the deadbolt working and you have two places for keys? Sounds like the handle flopping is the main latch that has a vertical handle?
What I have seen is using an angle grinder to cut from the outside until you get enough of that material removed to to hold of the latch inside to pull it loose!
Radical but I think you may be down to that and it may not be as bad as it sounds if you have the grinder available.
The door latch is what I call "pot metal" as not really very good quality steel but much softer and easier to form, which also makes it easier to cut!
Part number 8 goes through the door where I put the red X and is screwed from the inside to part 7. There are several (3-4?) "studs" built up on the outer part that meet the screws from inside.
If you have a grinder with a small blade, it is possible to nibble/grind off enough of the outer part to get those studs cut off the outer part. That leaves it loose to remove!
Not tough metal and you do have a 4-5 inch hole to work in but it takes care not to let it slip and run wild across the door face!
Best if the deadbolt is clear but if needed, it can be cut also as it is part of the new handle and I am sure there are replacement handles/locks around.
If I were going radical like this, I would get a new one, to see where the screws go and try to save as much cutting by spotting those before starting!
A second way is to drill a hole straight through and use a metal blade in a reciprocating saw to saw it clear.
Sorry!
But I think you are in a mean disaster that requires radical moves!