regeneration of wave function

San K

in a double slit single particle interference experiment:

when we try to find out which-way the "wave-function collapses"...however does the wave function "start to form" again once the photon/electron leaves the slits?

or is sending sending the photon through another set of double (or triple, quad etc) slits/paths the only way to regenerate the wave-function?

we know that a wave-function is a mathematical/theoretical tool and no one knows what happens in reality yet...however how is the wave-function regeneration mathematically/theoretically viewed within the concept?