Transponders also have a limited range, it "responds" to radar requests. A standard transponder does nothing when not in radar range. The ELT (emergency location transponder) can do linking to satellites, but not so well from under water... and it is only activated manually or on hard impact, at which point it might be damaged beyond transmitting.

Also, it should be noted that in a severe hail or severe thunderstorm, the GPS and NAV/COM antennas could easily be broken off or rendered inoperable, making the systems significantly less useful. Even if they are not, a severe TS can cause some big noise on a VHF system when it is close enough.

So, you lose those you basically have dead reckoning to work with, but with severe turbulence messing with your static and pitot systems, your altimeter, attitude indicator, climb rate indicator and airspeed indicator start jumping all over the place, and knowing how long you have been doing exactly what gets quite confusing. Especially when a large portion of your attention is to aviating through the severe weather.

So, no, it isn't easy for an airliner to get lost, but it can happen. And when it does, s#!t runs downhill fast. And it could be done with significantly degraded comms.