If the nut is stuck, I sympathise with the %$#@*
To avoid any further damage your choices are limited, either get it really hot (Oxy-acet) or split it
Check your threads afterwards. get them chased if required.
I don't know about replacing bearings in this case, but I suspect you will have to check preloads etc and ensure the correct size shims are used. probably the seals, if any, will be goosed too.
Sorry to be the bearer of bad news, good luck
Malc