Is the Ukrainian plan to take Donetsk and Mariupol areas and split the Russians onto 2 groups?
I'd suggest that would be a good plan (as long as logistics can support the long arc of supply).
Having drawn a large portion of the 'elite' russian forces and others to the Kherson region by disinformation, if the russian supply lines can be cut by getting to the Black sea coast at Mariupol and then turning/advancing west, then all the russians west of that cut ... are cut-off effectively.
The russians around the Zapo nuclear station (top right of yellow area, to right of large blue river - see below) are trapped, and can only retreat/fight through via Crimea.
The russians around Kherson are trapped and can only retreat via Crimea.
The pinch point at the top of Crimea (if you look at a better detailed map - ha! - there's only narrow bits of land joining the rest of Ukraine to Crimea), would become a kill/surrender zone as the russians try and retreat (if they are ordered to...).
The Kerch bridge would then become another massive pinch point for the forces in Crimea + any of the retreating forces that make it.
So approx:

Yellow: under threat russian forces
Red arrows: possible Ukrainian advances
Purple crosses: pinch points.
Edit:
@SPIDERBOY Seems to indicate that Mariupol is the target :-)
edit2: If Russia gets out of Crimea, I doubt they'd be able (within lifetimes) to get back in, as Ukraine will festoon the Crimea coast with anti-ship missiles, so any sea-borne invasion would be wiped out. An airborne invasion - would end in a similar fashion. Putin, if the war continues as it is, has just from a military perspective effectively put a highly sophisticated determined armed force directly on his border for the 1st time since the cold war - all by his own actions. Lost a large portion of control of the Black sea , bottled up his ships/ports to the Sea of Azov (the Kerch pinch point). Reduced his elite troops and elite weaponary to fractions of it's previous strength. Wrecked the officer corps of all 3 armed services belief in their commander's and commander in chief.