First of all, there’s no possibility to run the X1 (mk1/mk2) into the ipad at the moment, only the Z1, S2/S4MK2 will do the trick.
I bought the Z1 as a backup, too. I find it more convenient than using only the iPad.
Although the Z1/X1 combo is pretty small, i would miss the jogwheels – but if you’re happy with two decks and sync everything, you’re good to go.
In your situation i would suggest the following:
Upgrade to an S2 MK2 and ditch (or not) the Z1, carrying only your S2, laptop and iPad around. This way you can swap out the Laptop with the iPad if your PC crashes and have pretty much the same functionality. You could even leave the Laptop at home, only using S2MK2 and your iPad. And you can always use your iPad only, with a splitter cable, as a Backup.
I have an S4MkI and always have the iPad & a splitter cable with me. I also have a Z1, which I use mostly for small gigs like partys under the sky, impromptu gigs and for having a portable DJ setup when i’m travelling and can’t go without some mixing 😉
Hope it helps!