Any member or party can boycott parliamentary sessions.

However, there is a limit to missed sessions when a penalty is imposed on the individuals.

The PPP can do what they want.

But if they miss 3 sessions of Parliament, they will cease getting pay and can be brought before the privileges committee.

Them PPP C00olie like MONEY.  They will not dare boycott.

Good question.  And how is Article 164 (?) to be interpreted with  regards to majority vote and 2/3 votes in terms of amending the constitution?

Any laywer/liar on board here

It will be foolish for them to do that,they did that in

for some time in 1964 -1992.

Referendum on changing the Constitution.  No need for the PPP.

I don't think Granger really want the constitution amended. He can always blame the PPP for not voting. 

In changing the major sections to the constitution, it requires, at least, sixty six percent approval of the MPs.

Similarly, on another note, if the President does not approve a bill, it can be returned to parliament for another review. If more than sixty six percent of the MPs approve the bill, the president is obilaged to then sign and approve the bill.

D_G, how and when does a referendum takes place? 

Generally, referendum  can be held to address issues in the constitution.

2/3 of what votes?  Suppose the PPP is not there...Is it 2/3 of members present?  Suppose it is 2/3 of all members and the PPP stays out what happens?

2/3 of the 65.

It will be foolish, then the 49% that voted for the PPP will not be represented in parliament.

PPP parliamentarians are a commodity. Ever watch The Price Is Right?

They will not boycott.  They need the $$$.  Gravy train has dried up.