They made them redundant already by rewriting everything in systemd.

>> What will happen to the Red Hat Enterprise Linux product if they cut all the knowledgeable grey beards?

Inefficiency, which will spread to customers, who will then need more products and services?

They won’t do that

The product will degrade and customer service will worsen, but all RH's institutional/government customers will stick with them anyway because they have policies mandating the use of RH. This will cause RH to be more profitable, and their execs to get bigger bonuses.

It is possible (but certainly not guaranteed) that eventually, after years, some competitor to RH will arise and get enough of these customers to switch to make a real dent in RH's profitability, but by then the execs will be long-gone and cruising on their yachts.