OK so I dont quite get this one.  A general dies.  So a pro general returns at the beginning of movement and an instinctive at the end of the turn.  My question is why does it matter?  Neither receives cards nor can be given any as that has already happened.  So apart from the pro throwing themselves back into combat what is the advantage?

It also states that actions can be prompted with an extra card whilst he is away but where do the cards come rom and who is doing the prompting - especially in an 'irregular' army??

The new general exists and gets cards as normal, they just don't get to show up to the battlefield until the specified time. They can play cards while off table, counting as out of command.