If we take the shuttle bus and get off at a few different stops will it be hard for us to find a bus with room to return to the entrance.
Who is we? A couple, family or a party of 12? Usually it is no problem to find a bus with room for a few people. Keep the schedule handy. :)
We, and most passengers, remain with the same bus. Enough pit stops along the trip were provided. Neither my wife or me were interested in doing any hiking, as in our younger days we did backpacking into the wilderness.
But, to answer your question, I can't remember seeing anyone turned away due to a full bus. One thing for sure, you will not be left behind for the night
I was on a Wonder Lake shuttle the third week in June. On the way back we filled all empty seats at Eielson and then did have to turn away, pass several people along the road hoping to get on (at least 2 pairs and one group of 3). The driver said he would let the dispatcher know about them which he did when we reached the next rest stop.
I have stood in the rain waiting for a bus, last time third bus had room for 2. Still worth it. Come prepared u never know when it will rain or snow.