804 sounds about right.
There are 40 titles on Henry's list without heirs, but an analysis of that information shows the picture might be slightly less dire.
1. Westminster, Harlech, Hawke and Rossmore are all 40 and under, so there is hope for offspring.
2. Abergavenny will become an earldom from a marquessate, but there will still be a peerage.
3. Clancarty viscountcy will disappear, but there is still the earldom.
4. Powerscourt barony will disappear, but there is still the viscountcy.
5. Sudley barony is a subsidiary title of the Earl of Arran
Brooke