Very out of character but I don't think he should be blaming himself. He did everything he could for Richard in the weeks leading up to his death and he had no way of knowing his brother would die that day. Plus he rang an ambulance straight away and tried to do first aid/CPR. It seems sad that Richard should die alone on the floor but he knew Roy was coming back soon, with a signed football programme, he knew his daughter was back in college and he knew the two of them were starting to get on well.
If Aggie had been able to cook (and how long will that running joke last, considering she works in a cafe?) Roy would have been happy to leave her to get on with things. And, of course, if the carer had turned up he wouldn't have worried about leaving him. Plenty of "what ifs" when you think about it but if the cause of death was a heart attack Richard would probably have died almost instantly so maybe Roy couldn't have saved him anyway.