What protocol should be followed after accidentally entering restricted airspace with a UAV?
Well this one I can answer even without being an expert on India's airspace regulations: Entering a "no-fly zone" or other restricted area with an aircraft - even an unmanned one - is going to be some kind of a violation.
You local authorities could tell you what kind, but it doesn't matter: it's a situation to be entirely avoided.

You should plan your test flights to occur far, far away from such restricted areas (as well as from airports, population centers, "open-air gatherings of people" (to use the FAA's parlance), or anything else that you might disturb, damage, destroy, or annoy during your testing.
This is almost certainly what the DGCA is going to tell you if you contact them and ask for advice on test parameters for an Unmanned Aerial Vehicle, but more importantly it's just plain good old fashioned Common Sense!

If you cannot exercise such common sense you should rethink &amp; rework your plans until you can.
If after real, honest rethinking you're still in a situation where you feel you may inadvertently penetrate controlled or restricted airspace then coordinate with the agencies that handle that airspace PRIOR TO YOUR TESTING to make appropriate arrangements.



Now if you exercised all due common sense and still the absolute worst happens (Murphy's law rears its ugly head and LITERALLY everything that can go wrong does - even the engine cutoff and the emergency self-destruct didn't work!) you may still accidentally wander into airspace you shouldn't be in.

If that DOES happen your procedures should be effectively the same as they are in a manned aircraft anywhere in the world if you encounter the same situation: Communicate, Confess, and Comply.
Contact the controlling authority (e.g. tower, approach, the military division responsible, etc.), let them know what's happened, tell them where you are (in this case, where your drone is - they'll likely ask you to copy a number if they want to find out where "home base" is), and comply with any instructions they give you.
(This may mean you need a radio and a list of frequencies on the ground with you - picking up a sectional chart would be a good idea. You may also need a radio-relay in your UAV depending on what kind of range the vehicle has...)

Yes, the controller might get a little snippy with you (you are after all somewhere you're not supposed to be. Controllers tend to not like that!), and you might get in a little trouble for the violation (because again, you're somewhere you're not supposed to be), but that's all preferable to the potential alternative of smacking your UAV into a plane full of people at 300 feet on short final to Indira Gandhi International Airport.
As with all aviation operations, safety must be your overriding concern.