The Pensioners party is splitting up and it looks like 3 of the 7 are forming a new party.
Israel has a list based election system. You don't vote for any individual person but you vote for a party list. Given that, it makes no sense to allow any Knesset member to leave his party and and form a new one. He was not elected and it is not his seat. The party was elected and the party should control the seat. If an MK doesn't like it let him resign. The current system is the worst of both worlds. There is no personal accountability, you cannot vote anyone out of office, if they are high on the list they will be in the Knesset. On the other hand the MK's can do whatever they want with the seat once they get it. This is a formula for disaster and is anti-democratic (remember Sharon and Kadima).