Um....legally they can't just up and fire you after that.
If you have a medical condition, that is documented to have been caused by your job (and thus able to be the basis of an L & I claim), and said condition prevents you from being able to perform the duties of your job, then you must be declared "Disabled."
Once you are officially disabled, then your employer must attempt to place you elsewhere internally and retrain you to perform a new job. If they do re-place you within, they must pay you at least the same rate. If there is nothing you can do for them due to your disability, they can terminate you, but then they must pay for you to be retrained externally in a field with comparable pay.
That having been said, it is very difficult to prove that a mental condition was caused by any kind of on the job stress. Nearly impossible. It is very easy for L & I to deny your claim, at which point your recourse is to take them to court. If you loose (most likely outcome) you pay for your lawyer, their lawyer and court costs.
Also, if the person has ever been treated for anything related to their current illness, and it wasn't documented as on-the-job, your claim will be denied as a pre-existing condition. If it was documented as job related, but the person has since moved to a new employer, the claim will be denied.