Once Squad Commander's last ability has resolved, the affected creatures won't lose +1/+0 or indestructible if you no longer have a full party.
Squad Commander
To determine “the number of creatures in your party,” check whether you control a Cleric, whether you control a Rogue, whether you control a Warrior, and whether you control a Wizard. The number is the total number of those checks to which you answered yes. Each creature you control can be counted for only one of those checks.
Some cards refer to you having a “full party.” This is true if the number of creatures in your party is four.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Ekaterina Burmak
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