I’d say he’d be welcomed back. He did Jerry’s Comedians in Cars Getting Coffee and the curb episodes with larry david which suggests Jerry and Larry are happy to work with him. If Jerry wants to do something, a network would let him. I reckon if he came to them with a show based on live human sacrifice, they’d let Jerry do it.
As for Julia, she’s brilliant on her own show Veep. I’d bet if Jerry asked, she’d do it without a seconds thought.
Having said all that. I hope the rumours aren’t true. The original was timeless, and the Curb your enthusiasm tie in was an excellent final taste of the gang.