WI: He had died young, before attaining his majority? Who would have suceeded? Would a civil war have broken out?
Phillipa Plantagenet would be the official heir. In 1377, when Edward III died she was an adult and had two sons, so there'd be no regency or administrative council needed. This might actually free up John of Gaunt to press his claim to the throne of Castille.
But both she and her husband are dead by 1382, leaving her 7 year old son as King Roger. I'd expect a regency or adminstrative council dominated by John of Gaunt. John never actually revolted against Richard II in OTL, so he's unlikely to do it in TTL.
And Roger's OTL death in battle is almost certainly butterflied away. So long as he doesn't antagonize his cousin Henry Bolingbroke, his line will probably continue on the throne and the Wars of the Roses will be butterflied away.
Of course, the Black Death adds a certain element of pot luck to this.