Exiting and Returning to Vietnam ON THE SAME DAY to renew Visa

As long as the dates on your new visa are OK, then no problem.

Thank you Colin.

Is it possible to directly take the onward flight without going through the Thai immigration and leaving the airport? Please let me know, I'm stuck.

.

Yes!    Thai airports have their own accomodation for travellers-in-transit,
and Thai immigration allows a 15 day buffer to allow you to leave the
airport anyway, so relax; you are covered

..but you must still go thru immigration to submit your proof of being
'in transit'...     You must still get the Thai arrival stamp in your passport

  A small arrival/departure card should be available so you can fill it out
while in flight.   Ask flight attendant or counter staff to provide it
.

Thanks man. Your reply helped a lot. I was already in the airport when I wrote the question, and you saved me a great deal of time on spot.

Everything is under control now. Appreciate your help. The Visa run sh*t is not cool though, I don't think I'm gonna do that in the future.