you might want to add in an extra 2 vars. %rnlow 1 %rnhigh 1000
then when they guess too high it changes the high number to the one they guessed and the same for too low.

ex:
%rn = 500
guess 300 ... make %rnlow 300
(msg number is now between 300 & 1000 - so many tries)
guess 550 ... make %rnhigh 550
(msg number is now between 300 & 550 - so many tries)

completely up to you though.
As for unsetting the game if nobody plays for so long, you should use named timers on each command so it resets the timers whenever someone uses a command.
ex:

timer_rn 1 600 msg # game reset through inactivity.
timer_rn2 1 600 unset %rn*
timer_rn3 1 600 unset %tries
etc etc

I don't use timers much so you may have to test it, but to memory it's fine like that, I put 600 for a 10 minute reset.
there is a way to use -u but I can't remember it this early in the morning.