Maybe that's one of the many things fixed in Tale of Two Wastelands.
I remember ages ago when I first played it, there was no other benevolent option, but I didn't have Fawkes with me back then as I'd failed part of his quest.
Earlier this year, I did a ToTW replay of 3 and NV where I brought him with me and was able to have him go in there, thus saving my character but being branded a coward in the epilogue lol