For the in-house WTS lawyers, exit options might be better than some other WTS "volunteers" but probably not as good as some think. From what I have gathered, WTS lawyers enjoy a high status within the org, even if they are paid at standard Bethel rate. Anyone who was in the org at one point knows how much status and prestige are valued. They also likely get to travel frequently on the WTS's dime.
A law degree can be a valuable credential, but there are plenty of unemployed attorneys out there, just like in most other professions. For those who have done nothing in their legal career but in-house WTS work, I doubt there is high demand at law firms or in-house positions for these folks and the skills they have developed. Some of it may be transferrable, such as real estate purchasing, estate planning, etc. But law is also a very reference-driven field. It is common to have to know someone, or at least know someone who knows someone, a classmate from law school, etc, to be considered for a job. At a minimum, employers will usually at least want to talk to references from prior legal jobs. I doubt the WTS legal dept will be eager to help defectors get new jobs.
The other alternative if you don't want to work for someone is to open your own law office, but that requires (1) a lot of up front capital, and (2) a way to attract clients, which if it involves advertising, requires even more capital. The bottom line is they are probably almost as dependent on Bethel as most other volunteers and it would probably take a lot to get fed up enough to break rank and try to hack it in the outside world.