Yes, if they all showed up, they could have a quorum, but they wouldn’t be able to conduct any business because you can only conduct senate business by unanimous consent or through forced action by cloture, neither of which would be possible.
The only thing they could do is force adjourment, but I’m not even sure that would matter, because it may be that the senate was still technically in session before the adjournment is closed. I don’t know if you can object to bringing the senate INTO session based on the absense of a quorum.
That is an interesting question though, and I think I’m going to hit up my parlamentarian about that.
How ever they could refuse to approve the journal for those days that a quorum was not present. Make the RATS prove there was a session.