I would like to know whether a senior Program Committee should attend the conference or not. I mean that physically being there.
Thanks in advance.
"Should" is a judgement call that I won't make. If you are the person and if you are new at this, I'd recommend that you go.
However, a large and important conference (in CS) might have, say, 30 people on the various committees. At the conference you will likely find about 3/4 of them in attendance. Not everyone, but most. Some will actually be presenters or session chairs.
But the Capo di tutti capi would nearly always be there.