Satyrn
First Post
Recall that access to dispel magic is not automatic for Demons and Devils, and if they have it they may not have a '4th level or above slot' in which to cast it to avoid having to make a role to have it work. It may just be a spell-like ability they have that is only cast at the minimum level.
Full Disclosure: I can't really recall anything about the demons and devils in the Monster Manual. I've custom made all the ones I've used in 5e.
But I'm not sure my lack of that knowledge matters here. The OP seemed to be talking about one specific, individual devil integral to the plot, a devil he thinks may need to be present for a satisfying conclusion.
I was trying to suggest to him that he should give that devil whatever means of planar travel it would make sense for that Very Important Devil to have.