Low. While it is extremely unlikely for any group of normal soldiers to bring down a Named of any kind in combat, the Squire is near the bottom of the pecking order as a Name. If a Squire is to gain any kind of victory against powerful Named, it must be through cleverness or luck, because they do not have nearly the same power as most other Named.
A villainous Squire naturally has the ability to raise undead creatures. However, this power can only allow control of one undead creature at a time. If the Squire is inexperienced they may only reanimate an animal that they killed personally and thus formed an attachment to.
The Squire is also extremely likely, perhaps even guaranteed to gain the Aspect Learn.
The Squire's Role is to learn and grow. It is generally considered as a transitional Name that it is expected that a holder will eventually outgrow and abandon for a better name when a vacancy appears, a formerly inactive Name is taken, or the holder decides to kill a superior for their Name.