Gary and Morgan would probably come back. It is a job in the end.
Gary's done everything from "The book of eli"/ Harry Potter and the upcoming "Robocop" reboot.
Morgan's part could be done in one day of filming.
Caine could do a cameo.
Why would you even need any of them except for possibly Oldman? It'd be easy enough to set something 3 years down the line, Alfred moved on after TDKR (he's going to stay at Wayne Manor and watch the kids??), Fox has retired (leaving a red-headed wheelchair-bound digi-tech genius in charge of Applied Sciences - woot woot!) and Oldman does the cameo, but the main police character is the head of MCU, characterize and cast as you will.
The above is merely an example of how with a teensy bit of brainstorming you could carry on with the continuity coming via the Manor/ Batcave/ Gotham/ Wayne Enterprises - and not much else.