Horses are tough an will come back from alot of things but only if the person trying to bring them back knows what they are doing an such. You can't save them all esspecially if you don't have the money too.
My friends pony coliced then foundered and they didnt have the money to treat her for it. They tried for a month keeping a close eye on her doing what they could when they could. My friend even carried water an feed to the horse because she would just lay down most of the day. But when she realized it was a lost cause (and it was...the case was seviere and it had gone on long enough that there was no hope even if they did suddenly get the money to treat it) she had her put down.
Sometimes its the best way to go...more people need to learn that sometimes its kinder to end things then prolong them.