Firstly, the equation you are using relates to changing direction of a moving mass and so far as piping is concerned, the flowing mass needs to go somewhere having changed direction. You will get a similar result from centifugal force and change of momentum equations. Both assume continuity.

If a slug hits a blind, where does it go afterwards ?

Are you assuming that the pipe is empty (a vacuum ??) upstream of the blind prior to arrival of the slug ? Or is there some gas being compressed ahead of the slug ? If so, where does it go to ?

This does not seem feasible to me.