I'm not sure why they made Indy get married, but I guess they have to roll with it some how. So...
Here are a few things that I think it could work.
Just get rid of Marian. As classic as Marian's character was, I would like to see them either kill her off or get rid of her some how in the next movie. You could have her already be dead or gone by the start of the movie. And then that could play into some of the character development for Indy and Mutt (if he's even in it). Also, I think it would just be a bit weird to have Indy's character be married.
Family Adventure. I'm sure that they could have some family fun with Indy, Marian and Mutt going on a family adventure, but it would be really tricky getting it to work within an Indy movie. Plus that was kind of already done with Indy 4 so you can't really do much more in that area.
Marian could be in it but maybe she just doesn't go along for the ride. This wouldn't be a terrible way to keep her involved as little as possible. Indy and Mutt go on an adventure and Marian simply stays home.
Anyways, In my opinion, I'd prefer them to not have Marian in the next movie but I know that they've kinda written her back into the story in a big way so what ever happens they would have to tie up some lose ends if they get rid of her all of the sudden. If there is anything that bothers me in movies its loop holes and killing off characters just because they can.