I see the mind thinking as no more than the eye seeing or the heart beating; it has a function for the organism that if in giving a greater chance of survival lives on because of this advantage in the success of that life.
Everything you see in the room around you now is made up of the atoms described in the periodic table, a relatively small amount of atoms combined to give complex physicality to the metals plastics wood and glass and so on. The body of flesh and bone and blood is also chemically made up of the same atoms in this table of atoms. The atoms in the table are no different from one another also but merely have greater or lesser numbers of electrons.
If I stand back from this picture now armed with this knowledge that everything is just a collection of atoms and the atoms themselves only differ because of the amounts of electrons I see how in all our complexity we are just a collection of a common stuff.
So a mind is born lives for a time then dies, it is just a collection of atoms, but if one atom is no different than any other, then one mind is made of the stuff all minds are made of. The mind starts like a movie at birth and plays out its individual evolutionary tale till it dies, but if the stuff all minds are made of is all the same the individual watchers are also all the same.
I can see that every life is like a individual movie and that every movie has a watcher, a watcher that is the same as every other watcher.
This would mean there is only one watcher of all minds but this is not saying that there is a single mind just in one place somewhere but rather that there is a single mind in every one of us being watched by the same watcher.
When you are born it is just another mind to watch and when you die it is just one less mind being watched by you.