Relax. I was in a similar situation, but did not have the inclination to go ask my previous employer for Form 16. You need the old employer's Form 16 only if you want your new employer to file returns on your behalf. Instead of filing my returns via the new employer, I filed it myself showing only the Form16 given by the new employer. It took hardly 15 minutes. It of course meant that I'd not declared my income for the year spent with the old employer, but I'm no millionnaire and so IT dept does not check at this level of detail (they're Indian government employees, after all!)
Unless you're a really rich guy, you can save a lot of hassle by not bothering about the old Form16 at all.
