Even under the best of circumstances, if every league gets everything aligned in such a way that makes playing as many games as is feasible a realistic possibility, there is still one final task at hand: getting as many players as possible to be willing to play through a pandemic.
The inevitability is that not all will play. We already know this, because several players in the MLB and NBA have already announced their decisions not to play, and the NHL has already said that they fully expect that some of their players will not play as well.