What happens if someone has entered US in B2 visa valid until 2019 and applies TPS:
.
will his multiple entry validity be vanished and has to reapply for visa even before 2019 if he goes back to Nepal after TPS period is over?
will applying for TPS affect his chances of getting visa again after his visa expires?
what happens if his decision on his TPS application not made by the USCIS by the time his I-94 validity period expires?

Thank you

When did that person come to US, I hope it was before/On June 24th.

TPS does not conflict with any other status. If TPS expires before 2019 then, he/she can go back to Tourist VISA.

I am not 100% sure about the status of the person when case is pending. Without TPS that person can not live after that I-94 period, but when TPS is applied and USCIS gives the case number, then it should be ok (not 100% sure). Why don't you talk to any lawyer?
Good Luck

Just give a call to USCIS, but I am not sure if they reply these kinds of question.

Thanks MimroRaMero....
Any other suggestions?

You are welcome,

I have raised the question here, let's see if we get any answers.
http://sajha.com/sajha/html/index.cfm?threadid=113759&noofposts=41