if you can't continue the game and you have not home-grown talent, go on holiday (i don't know if this will work) or edit 1 player to be home grown, try to choose a reserve player for this, you don't want Fernando Torres playing for England in the World Cup
I imagine if you didn't select the maximum amount of players and you don't have enough in your reserves, then the extra places will be filled in by shaded hg players once you come around to the game.
If you only need 1 more home grown player you can only select 2 and the 1 player you havnt selected counts as a homegrown. If you are 2 short only select 23. And so on...