Should they've let rue live with katniss and peeta?

No. It was a miracle to have Katniss and Peeta win, Rue would just complicate things both politically and emotionally-districts would be asking for their lost tributes and uprisings would begin, which of course the Capitol was so determined to avoid.

No...

No cuz then katniss wouldn't hav a reason to b upset about something...hope tht doesn't mak me sound insensitive

No. If آپ start going down that road, آپ might as well say that they should have spared every tribute. It's meant to be part of the tragedy.