I'm now preparing for GATE Only for NIT or IIT. What if I do not get admission?

#-Link-Snipped-# Why is there no chance? Have you tried taking a mock test for either GRE or GATE? What is your current score? If you share some of this information, we can tell you the kind of preparation you need to crack these exams. 

Your question right now is quite vague. Please add complete details about what is your confusion.

#-Link-Snipped-# - While setting up a high aim is a good thing, you should not absolutely rely on getting admission into NIT or IIT. Take as many national level mock tests and see what rank you get. The rank in mock test should give you an idea about the competition and where you stand in it. If you are getting rank 'X', you should see if X - 400 can get admission into NIT or IIT. If yes, you have a pretty good chance of making it to the top institute. 

Otherwise, be ready with a backup plan. 

GATE preparation studies are going to be vastly different from the preparation for MS from a foreign University. You'll need to have ability to crack aptitude tests, have an above average command over English language and also have logical reasoning ability. Do take a look at preparation material for GRE and TOEFL and you'll understand what I'm saying. 

However, even with a lower rank in M.Tech, you should still be able to get an admit into a decent M.Tech course in India. Your mock test scores should give you a good idea of which college you can get into.

Hope this answers your question. .