How to know if a node is connected to another one ?

[deplanty]

This request is quite simple (I hope). I'd like to create a Node that splits equally things in the output.

Here is an example : I have a value that outputs in 3 nodes.

And I'd like my outputs to update when a node is disconnected, as follow :

Is it possible to achieve this ?
How can I know if my output is connected or not ?

I have another question which may be out of the subject : can I restrict an output to only one node ?

Thanks !