Hi Eliza
Just to keep your post alive …
I think it is better to remove the slabs.
If you have 2’x2’slabs you could lift a few to give a 2′ wide bed, and also scrape out scalpings/sand/mortar or whatever the slabs sit on; removal of slabs and foundation will give several inches extra depth and easy access to the soil below for the roots of your crops. Removing a double row of 18″ square slabs would give a 3′ wide bed. If the line of your service pipes coincides with your new beds and the pipes are encased in a few feet of concrete then you will have no soil to access but this is highly unlikely.
If there is access to soil below I doubt that you will need deep raised beds and one could argue, in a best case scenario, that removal of slabs and foundation would give enough depth for several inches of compost over the soil with no need for a raised bed. It all depends on what you find below the slabs.
There is fear of roots interfering with underground water pipes but, as long as you intend to grow annual veg rather than a willow plantation, all should be ok.
Good luck with your project