My guess is they will try quite hard to sign Monahan. I expect they'd like Tofolli as well, but they have plenty of wingers really, too many almost. Monahan fills that need at center and if they sign him for five years it addresses a substantial need.
Not sure who they see as the youth movement for the center position in the future. I'm fairly certain they were hoping Lucious would grow into it and he may, if he ever overcomes his injury woes (hoping the surgery does it). Otherwise for middle six guys their looking like they're going to try and convert some wingers - Lambert, McGroarty, Perfetti? Zhilkin probably doesn't have that ceiling.
They don't have the cap space for both. It's one or the other imo and they already have a lot of cash tied up in wingers that it makes little sense to keep Tyler if they plan to reup Ehlers.