Fleets will not fight to the death, at some point someone will break off or surrender, so total damage cannot be easily calculated.
See that in my quoted rough example I assumed some of the losers flee the system...
The damage (& cost of repair) from a single hit can easily be calculated (with some basic assumptions).
A Meson J that inflicts damage does 10 hits on Rad and Int tables presuming the target is large enough to avoid size crits. With statistical combat resolution that means 100% chance of a Fuel Tanks Shattered. With rolled damage that means 1 - (1 - 4/36)¹⁰ ≈ 69% chance of a Fuel Tanks Shattered. An average of 4.3 Crew hits will be achieved.
The rolls on the damage tables will lead to an average of 1.94 crits which will lead to 5% chance of Ship Vaporised plus a 51% chance of mission kill through loss of drives, control, or crew.
The target's chance of not being mission killed is about 16%.
For a Meson T there is about 89% chance of Fuel Tanks Shattered, 10% chance of Ship Vaporised, and 3% chance of remaining combat effective.
For a Meson T against a 50 kT ship (code P) the extra 4 crits leads to a total of 21% chance of Ship Vaporised and on average 2 mission kill hits.
Setting a price tag on each hit we can, with some work, calculate the average cost of repairs per ship class.
Another factor that is usually ignored in most TCS like calculations is crew quality. In HG, having a CO with Ship Tactics 3 raises the computer rating by 1, seriously altering them foth in ofensive and defensive way, and a pilot with skill 3 raises Agility by one, making it harder to be hit. And if the skill is at level 5, the modifiers are +2.
While this will have limited effect in a battleship (or Battleriders) battle, against hamsters it may well be decisive.
If we make some silly assumptions such as every battleship is in a battle twice a year, each ship fires 3 times in each battle we can estimate attrition rates. A 200 kT 6G Meson T battleship has a 42% chance of hitting itself, or 72% at short range. It has a 81% chance of penetrating, so each ship will produce something like 2 × 3 × (42%/2 + 72%/2) × 81% × 13% = 0.36 Ship Vaporised results each year. Under such conditions attrition rates for battleships will be in the region of 33% per year. To that we can add ships captured during repair and scuttled rather than transported to a distant enemy yard. The rebellion is supposed to be a bloody affair...
Accepting your numbers, see that this would mean the BB fleet would son be attrited, but the BRs one probably less so, as they are very rarely so scuttled, being taken to repair shipyards by the Tenders, some of whichwil lbe left without their BRs by own losses.
And even the BBs can in most cases perform field repairs and go to the repair yards by their own powers, if they can be crewed...
OTOH, while not explicited on the rules (in fact, not even mentioned), I guess we can assume the tneders would have some repair capability, at least for their own BRs...
So, I'd say the fighter fleet (and probably escort one too) would quiclky be attrited, the BB one slowly so, and the BRs one very slowly so. OTOH, being smaller, criticals would be more numerous, but I guess the large BBs with larger Spinals would be the first ones targeted, so the first ones crippled, and soon the BRs would be all left to fight.
But the main point, following my reasoning that most loses are repairable, is that "keeping the field" is a critical factor in HG combat, as you can recover most of your "killed" ships (as most would in fact be crippled) and capture some of the enemy's, so even increasing your fleet instead of attriting it, while the loser really loses most of them. So, the victor can end the battle reinforced, while the loser heavily weakened.
Again in my quoted rough estimate aboe, see that the loser would loss all the escorts and msot its BRs, while the winner will end with one each destoryed, but capturing several of them (so ending with about 4-5 escorts and 7-8 BRs more than it began the battle, albeit crippled ones, but easy to repair...
In this sense, it is (again) like the Age of Sail, where wining a Naval battle used to mean prizes to be won, many times increasing your fleet numbers more tan what losses could reduce it.
And see that Rebellion was assumed on MT paradigm, where the lack of agility for most Battle fleets and different use of Ship Tactics skill make hits more likely (but again, most would be crippled, not outright kills)...
Which HG are we talking about?
I assume HG2, unless otherwise said.