If ROTC is having you take classes, they will pay for them. Where this gets somewhat nebulous is if some schools decide to go fully online, postpone classes, etc. no one is really sure how ROTC will react. I recall that AROTC had proposed several different plans if schools are online, such as delaying training, having ROTC students be on campus despite online classes, or even having individuals train at their local unit while taking online classes.
The short answer is that no one really knows what is going to happen. Even the schools that have stated they will be open in the fall have not said exactly what that is going to look like. The one thing I would be confident in saying is that if ROTC is having you take classes, and you meet the activation criteria (fitness, grades, graduating high school, etc.) then they will pay your tuition. Past that, I, nor anyone else, can really say exactly what the fall is going to look like, as this is a fairly unprecedented situation.