Will half and half work instead of heavy cream

From a fellow lactose intolerant person, FYI, heavy cream has very little lactose (which may be why you can buy lactose free half and half, but not heavy cream). In general with dairy products, the higher the fat content, the lower the lactose. This article explains: https://www.healthline.com/nutrition/dairy-foods-low-in-lactose#TOC_TITLE_HDR_7

Yes.

Naturally the sauce will lose some of its unctuous rich texture.

You could use half-and-half, milk, or even a non dairy alternative (like almond milk). At least one recipe commenter here at Food52 said that coconut milk was a successful substitution.

Yes, half-and-half should work to replace cream in this caramelized leek pasta dish. I'd expect the end result to be somewhat lighter, which to my mind, could easily be an improvement. You might want to adjust the amount - perhaps adding a touch less at first, checking the consistency of the sauce. ;o0