Do we think Howland Reed will play any role in the remainder of the show? I definitely think that he will play an integral role in the unfinished books but at this point I do not know if they have room for him in the show.
Maybe he will be needed to convince the Northern Lords that Jon is Rhaegar's son, because they might not believe Sam/ Bran. So, Howland, as a Northern Lord himself, can confirm Jon's parentage and by doing so put an end to the Northern Lords bitching about a Targaryen (Dany) being their Queen seeing how they elected a Targaryen (Jon) as their King.
Maybe the battle of Winterfell is lost by the living and they need to retreat South. Eventually meeting up with Howland and gain some insight on his experience with the Isle of Faces. I personally feel the Isle of Faces will be a key location for a some type of major event like a truce with the Walkers (like the pact between the Children/ First Men), killing of the Night King since that is probably where he was created by the Children or something significant.
Either way, I always found Howland's character intriguing and thought that he would play a more important role, especially with unveiling the truth about Jon's real parents. At the very least bring him up for the battle of Winterfell along with Meera because Jon and co. can use as much help as they can get.