My mum died about 4 years before I got pregnant.
I was living 200 miles from my old home anyway so I suppose I didn't actively miss the day-to-day practical help someone else might have had. It was mostly the regret that she wouldn't get to enjoy her grandchildren (one of the first things MiL said to new baby was "oh, she would have loved you...").
As with everything else, you have to get your advice and chat and cheerleading from other sources, and put up with the fact that they're not as invested in it as you are. It's not great, but it's ok.
I do think I grew closer to MiL once the boys came along, which might not have happened if my mum had been around (would have asked mum rather than MiL to stay when S2 was born, for example). Of course the success of this will depend on your in-laws - mine were great (FiL gave up smoking while I was pregnant, they respected my views on smacking and extended breastfeeding and weaning without added sugar, and bought magazines rather than sweets).
It can be done. You can do it.
Boys are 21 and 18 now, and talk quite matter-of-factly about their other grandmother who died before they were born, which I find quite weird (and makes me wonder whether I used to make my mum feel bad talking about my dead grandad...)