so, i had a lawyer look this over AND consulted with an ex-viacom legal employee (lawyer). technically they can revoke the severance with this clause if you notify them (unsure about how the amounts work if your new job pays less than what you are being paid out by viacom). HOWEVER, this clause is not really enforceable, you do not need to notify them of new employment (and they have no way of finding out if you keep it to yourself/off social media), and lastly, the viacom lawyer told me in her career at viacom (14 years and also laid off), she has never seen them enforce this clause (it would make for bad press for the company, and they want to seem very pro-employee/great place to work). she said the purpose of it is for high profile executives who may accept another high profile role. i have plenty of viacom ex-employee friends now collecting double paychecks.
I'm glad I found something on this topic on this board. Useful info, no doubt. Thanks, OP @VNIe3jG-1pwo