The main benefit of hydrogen is that refueling is quick, using a system similar to that for CNG. So a H2-powered vehicle (rail or otherwise) can be back on the road in about the same amount of time as a liquid-fueled vehicle (diesel or gasoline) that needs refueling. And unlike a battery which under present circumstances may take a 1/2 hour or more to fully recharge.

H2 is usually used with a fuel cell, resulting in zero local emissions (except water). Where the H2 comes from is the real issue; for now, most industrial H2 is produced by reforming natural gas, which releases considerable carbon as CO2. It's certainly possible to produce H2 by electrolysis of water, or even running a fuel cell in reverse, but the energy needed for the process is considerable compared to charging a battery. It may still make sense, in restricted applications (like some of the German H2-EMU projects in relatively remote areas, where solar panels produce the power to run the electrolysis systems, producing hydrogen to power the EMU.

The issue of tank life is real, but minor, and is due not to the pressures involved (CNG tanks run similar pressure and are good for the life of the vehicle) but to chemical activity. H2 weakens metals exposed to it and can't be adequately contained by a plastic tank, especially at high pressure. But the tanks are fine for at least 10 years. Tank replacement can easily be a standard part of mid-life or 1/3-life (assuming a 10-year major service interval and a 30-year vehicle life) service procedure.