This is an interesting issue that I have come across many times. If the track opens up, and the rhythm guitar track is lost during the solo, then something needs to be done. Yes, a solo part feels best to me, out front and center. But, if it affects the mix, and becomes a 'drop out' in the feel of the song, then adding another track would be best. If this is a finished recording, and adding a new track is not possible, then there are ways to work around it.
Back to the unfriended, and typically thrashed upon theory of duplicating a track, and delaying it to create a image on the side needing a hole filled, I will do this to keep the space filled, with the other guitar track during the solo. It really can work, though I don't recommend this as a starting point. Only a fix that can actually work when needed.
Expecting some thrashing now.....