Have a look at these 2 functions
here and
here.
It'll only return false if you're currently having some parameters pushed to the forward, that's it.
So as long as you remember to Call_Finish or Call_Cancel after all your Call_Push* you're good to go.
Also, aren't problems usually better dealt with after they happen? This seems to be a question that's asked in advance, for something that could theoretically happen, but hasn't seemingly been a problem for anyone ever before.