You could do any of the following:

A. Vote Dismiss them for AFK'ing. Though finding a new healer may be a bit difficult.
B. have the person they are following drag them into potentially lethal AoE repeatedly, thereby racking up their repair bill, significantly if they actually die.
C. stop moving until they come back and ask why there hasn't been any progress made.
D. Vote Abandon the Duty and try again with a different group.
E. Leave the party yourself. Yes you would have a 30 minute wait time, but as you are a Tank class, after that 30 minutes is up you will likely insta-queue. Basically all you will end up with is the equivalent to a DPS's average wait time as a one-off.