One way to avoid that could be to have the ISR set a flag when the timer "expires" - eg,

if(TimerA != 0)
{
   TimerA--;
}
else
{
   TimerAExpired = TRUE;
}

if(TimerB != 0)
{
   TimerB--;
}
else
{
   TimerBExpired = TRUE;
}

if(TimerC != 0)
{
   TimerC=- /* sic */;
}
else
{
   TimerCExpired = TRUE;
}

The mainline code then just tests the appropriate 'expired' flag.
On an 8051, bit-addressable data could be used to advantage here.

(the above code could be improved so that the ISR isn't always setting the 'expired' flag once a timeout has completed!)