Re: disability
Don't forget about the Americans with Disabilites Act ("ADA"). It applies to disabled employees of companies with at least 15 employees.
If your condition qualifies as a "disability" (as that word has been defined, for ADA purposes, by the courts), your employer must provide you with a reasonable accommodation. A reasonable accommodation might be a chair, the option to telecommute, or unpaid leave.
Unfortunately, what qualifies as a reasonable accommodation depends on the facts of the situation. A larger, more financially-secure company can more easily afford to give time off and hold your position open than a smaller company just scraping by. And it also depends on the nature of the business, and your role. If you are a key contracts negotiator, perhaps the company can go no more than a few weeks without you. If you're a forklift driver for a major Wal-Mart hub, it might be reasonable to hold your position open for more than a year.
So really, the answer is "it depends." It depends on the extent to which holding the position open for you puts the company in an imposition.
How long can you be off before being terminated? As long as it is reasonable for your employer to hold your position open for you.
And then there are comparable California laws, in addition to the federal ADA.
If things go sour, consider contacting the Equal Employment Opportunity Commission ("EEOC"). You can file a charge with them, and they can conduct an investigation, or mediate between you and your employer. Feel free to contact me if you have additional questions or need assistance.
