Your boss can terminate you any time he likes, as long as his reason is legal. But, the real question is, why would he? Usually people give two weeks notice. This is rarely enough time to find a replacement. Many employers would be thrilled if you came back and said: "Hey, you know what? We're not leaving until the end of February, so I can work until the 28th."
So, what is it that is keeping you from saying that?
Bosses are normal people. Sometimes they are mean and irrational, but most of the time they just want to get the job done. When you go to your boss and explain the situation, keep it in a positive light. State that you just found out that you can work through the end of the month, rather than the 15th. Then add on some key points as to why this is a good idea for the business. Your company doesn't really care if it's a good idea for you (although most bosses will because they are nice people). Your company cares that it's a good idea for them.
Here are some benefits to you extending your notice period: You can help with recruiting, you can train a new hire (if they find one), you have a longer time to transition responsibilities to others, and you'll have more time to document the unwritten aspects of your job. All of these things are a benefit to the company.
What you don't want to say is: "We're not leaving right away and I really want to get paid, and if I can't, then I'm going to file for unemployment." This sets you up for an adversarial departure. Remember, that even though you are leaving this company and this job, you want to leave on good standing. You will need a reference, and you don't want your boss's freshest memory to be your demands that he acquiesce to your desires.
If your boss says, "Thanks so much for the offer to keep working, but we have it under control," then don't pitch a fit. Politely thank him for his time and consideration. Go ahead and file for unemployment, but note that this is a situation where I would contest unemployment. (Which an employer can do.) Why? Because you resigned, even though you did so verbally. I don't know what the state would say, and ultimately unemployment is a state decision.
But, on another note, leaving your job to follow a relocating spouse can make you eligible for unemployment in some states. You might want to look into that while you search for a new job.
Suzanne Lucas has nine years of h uman r esources experience, most of which has been in a Fortune 500-company setting. She holds a Professional in Human Resources Certificate from the Society for Human Resource Management. She blogs at Evil HR Lady.