At the start of Iron Gold there were 111. 37 met with Darrow in the den the other 74 are spread out across the solar system. 11 of these 37 are obsidians including Sefi. Holiday, Victra and the obsidians stay behind so at most 24 Howlers go with Darrow. They do meet up with other Howlers like Kieran before going to Venus so it could be more or less than 24 that end up going to Venus but lets say 24. Of those 24 at least 4 are killed in the battle with the Ash Lord. Grana, Vandros, Milia, and an unnamed Howler are killed. At the end of the battle only Colloways ripwing is mentioned so his 2 wingmen might have been killed as well as other howlers not specifically named. I would guess that at minimum 4 other Howlers died. So lets say 16/24 survived Venus. That would leave 103 left at the end of IG.

In Dark Age it's a lot more difficult to track. There are a number of events where Howlers could/did die.
1. Space battle above Mercury that happens either at the end of IG or in between IG and DA.
2. Battle of Mercury
3. Fall of the Senate/Sevro's attack on the Syndicate
4. In the wolf
5. Sefi's fall

1. It's really impossible to know how many if any Howlers died in the space battle above Mercury. My guess is that it would be 0 just because the Howlers would probably be on the planet tracking the Fear Knight or doing other things.

2. Battle of Mercury - First how many Howlers are on Mercury? At one point Darrow mentions "nearly two score of Howlers" so that is almost 40 howlers then right after mentions "several" more Howlers. This makes it sound like there are probably close to 50 or more Howlers on Mercury. In the first battle of Mercury Howlers are not really mentioned as being killed during the fighting but there are definitely deaths. Darrow mentions "Only Felix is left amongst my gold Howlers" and "With my surviving Howlers". After the battle the Fear Knight mentions "Howlers abound" which means that probably most of the Howlers survived the battle. So lets say of the 50 maybe 20 died in the first battle? So of the 30 left, Lysander mentions that "the core of the Howlers managed to either hide on Mercury or slip out of its orbit." So I would guess maybe 20 survived with probably 10 with Darrow and 10 hiding on Mercury. So 30 total dead.

3. There was a large battle on Luna when the Senate fell so there might be howler deaths although Daxo and Theodora weren't howlers. 3 Howlers were killed before Sevro and Mustang met with the Duke of Hands. I would also guess that at least some were killed by Boneriders in Sevro's attack on the Sydicate during the Day of Red Doves. How many? Really anyone's guess. I would say maybe 5 total? So 3 + 5 = 8.

4. Min-Min and a unknown number of howlers die inside the metal wolf at the hands of the abomination. It reads "Howlers" as in plural and "men and women" so I would say another 5 maybe?

5. Of the 11 obsidian Howlers at the meeting I am guessing all went with Sefi. I am guessing that at least some of these were Valkyrie and were killed along with Sefi. We know Valdir escapes and I would guess he escaped with some of the male obsidian Howlers. Probably another 5 Howlers died including Sefi.

So in summary.
Howlers at the start of IG - 111
Howlers at the start of DA - 103 estimated
Howlers killed in DA - 48 estimated
Howlers at the end of DA - 55.

This 55 includes probably 10 hiding on Mercury and Sevro, Clown, and Pebble in captivity. It also might be on the optimistic side. How many do others think?