Resting Sarfraz for just 2 games isn't fair for him actually - he is Captain selected for WC, therefore if he comes back by 3rd game and PAK loses couple of the last 3 ODIs, he'll have very little contribution in that win or loss, but it'll put him under undue pressure. If they want to rest him, I think it should be for full series so that his deputy is also ready, just in case if Sarfraz is injured during WC. I would rather say, play him all 5 games as specialist bat and keep with Umar or Rizwan or a new guy. We have two WKs in playing XI and often in less important games Liton actually keeps and Mushi plays as specialist bat - Sarfraz can play as specialist bat at 4/5 and lead the side, which will take at least 75% of his physical burden. Just before WC, resting Captain partially isn't a good idea - they should have done it against ZIM reserves or against NZ at home.
Having sad that, I think it's a good initiative to rotate squad - at last. More or less, excluding Sarfraz, what I understand is 7 players will start for PAK in WC barring injury - Imam, Fakhar, Babar, Hafeez, Malik, Hasan & Shaheen, may be Faheem as well. Not sure about Shadab now, because if PAK plays one spinner - he shouldn't be ahead of Imad now & I am a fan of leg-spinner; but Shadab isn't doing anything to justify his status as automatic choice.
Ideally, in WC, PAK (any team) will need 30 solid overs from pacers, 10 overs of quality spin and 10 overs of a mixture between spin or pace depending on wicket + Sarfraz and 5 solid batsmen. Of the list Hafeez is out for injury hence it comes down to 6 - I'll keep Imam in the starting XI because he is in great form and at this time dropping inform young player isn't a good idea; Sarfraz remains as Captain, but as specialist batsman - and I'll drop other 5 for the entire series.
This will be my squad of 15 for entire series
Openers: Siddique+, Shan, Imam
Middle Order: Umar+, Haris, Sarfraz*, Saud
Spinners: Shadab, Nawaz, Irfan (leggi)
All-rounders: Amad, Yamin
Pacer: Amir, JK, Wahab
If Haris isn't fit, then may be Amin makes it. Also, I hope in at least one game Umar keeps, rest 4 Siddique should play (might not open). Wahab makes it strictly for WC in mind - one express pacer is required in squad. Amir plays to justify his spot rather than as an automatic choice while if they go for 16 players it should be either Shinwari or they might check Irfaaan as well. Amad comes in because in my squad all possible 5 pacers are lefti - I probably'll play both all-rounders in all 5 games and the better one makes the trip to UK, as Faheem's back-up. Imad is certain to make the WC squad at least, therefore no point picking him in squad, rather they should pick 2 Leggis and give both of them significant amount of games - may be 4 each. Nawaz is in brilliant form oblate - should be considered as the back-up SLAO spinner, no point considering Gohar or Asghar anymore before WC.
Total 55 spots (5 X 11), I'll give it like this regardless of the results
Imam 4, Siddique 4, Shan 4
Umar 5, Sarfraz 5, Haris/Amin 4, Saud 0
Shadab 3, Irfan 4, Nawaz 3
Amad 5, Yamin 5
Amir 3, Wahab 2, JK 2
Only Umar play all 5 games, because he is the only one who has a genuine chance of making starting XI, coming from totally out of sight for 2 years; Sarfraz obviously is there as Captain for 5 games. The 2 all-rounders get all 5 games because they are fighting for one spot - should get proper opportunity. Both of them must bowl at least 35 overs in the series and bat at 7-8. If it wasn't UAE, I would have reduced one game each from the 3 spinners and increased 1 game each for the 3 pacers. Saud is there for the experience - no way he is going to make it for WC squad now. In batting order, top 3 will not bat below No. 3; Umar, Sarfraz must bat at 4 & 5 (can exchange 5 to 4).
There is absolutely no reason why Malik will lead the side, in fact play because after 20 years, from 2 games he is not going to learn anything more. If they are certain to make him deputy for WC, then fair enough - rest Sarfraz and play Malik at 5 for all 5 games.