I think you're right that Trump would much rather sign off on appointments to the Supreme Court and let them deal with it than engage in the issue to any degree. Certainly, he would have zero interest in the constitutional arguments. And yes, even with a new appointment, there is not likely to be any overturning of Roe v Wade, as there would still be five justices who wouldn't go there. 

Trump is going to do the stuff he's interested in. He's going to get his lackeys to at least appear to do the stuff his base elected him to do. This probably doesn't include a single social issue. He isn't interested enough or empathetic enough. It's why marriage equality is probably pretty safe too.