This is one of those personal decisions only you can make. I think I would still ride my bike without front brakes for a short time if I had to. You have geardowns to get you slower and a back brake to add to your awareness. I would still put the master cylinder rebuild high on my list (as in asap).
btw - my riding style has me normally relying heavily on the front brake for stopping. I just feel as though awareness of the condition of the bike balances safety with risk. Ride slower, more cautious, and ready for it. Again, it's one of those personal judgements. My answer may not be the politically correct safety poindexter approach, but I'm giving my honest answer.
'91 VN750 - Cosmic Splendor/Candy Wine - 10k mi.
Done: Coastered, .020 ign., Iridiums, VM, Plexistar II, MCCT's
Will Do: MOSFET, Horns, Shave(maybe)