Your spark Lasts 52 weeks. So if your child is 48, then you'd get 52 on top of that. Of course you're not guaranteed that 52 weeks due to spirit loss upon Coup de Grace. So if you "die" a lot you'll lose more spirit doing spirit walks. However, if you have high fame you'll require less "deaths" to permadie.
It all depends on how you play, but you'll be able to have that life still. It'll cost more story points to spark into an NTC though so make sure you're doing things!