what event?
There is small chance milan falls into PU with anyone at 144x if they don't get heir.
its dependent on PU mechanic then. Basically they need to be at peace and heirless when their king dies.. then you can stuff like a succession war, or a direct inheritance.
the situation in 1444 needs to change; the POPE and+or the HRE emperor have to die (in total) a few times before you get different outcomes then dynasty spread into Ambrosian republic.