Yes you are in the right place, but the wrong file.
All caravans have a one-time only payout man, that show up in case the caravan master dies.
In Hal's case though, you only get the payout man (SCDRVPAY.SSL), Hal himself never sets foot in Redding.
Yes, Hal has dialog and outdated code for paying you, but that was abandoned by the devs at some point, and there is no code for placing him in Redding in the REDMENT map script. Also, in Hals version, he only pays you 150 plus 150 extra for each party member you may have with you (not a bad feature actually).
Anyway, "set_cattle_drive(CATTLE_FINISHED);" means "set_global_var(266, global_var(266) bwor 8);"
Now Gvar266 is a flag (bitwise), which means it can have several values at the same time.
Bit number 1 is 1, bit_2 is 2, bit_3 is 4, bit_4 is 8 and bit_5 is 16 etc. So if you look at Gvar266 in the save game editor and see that it has a value of 25, you know that bit_1, bit_4 and bit_5 is "on", and the rest of the bits are "off". A successful run should end with gvar266 being 797.
The problem is not that Gvar 266 isn't reset to zero by Duppo before the second run, as the payout guy in Redding can disappear anyway. The problem is that there shouldn't be a second run at all, and if there has to be one, then the payout guy shouldn't be told to erase himself.
I agree with you though, that you should be able to get into the Casino no matter what is up with the caravan (though I seem to recall that is a vanilla problem).
Also I don't think the double pay from fortune finder was ever put into the game, at least I didn't find it in Wade's scrip.
Also+ The payout guys for the regular caravan masters still pay way less than what the caravan masters do. I guess killap forgot to fix that.