Why? It's not directly exposed to flame, nor much of anything. If it works it works.

seems like it would be more apt to absorb water or wear out quick

It'd be the same as running straight gasket sealer, except the cord would give it some resistance to stretching. You'd just have to be careful to ensure an even and consistent coating.

exactly, you'd have to be extra super careful to do it just right, hella risky I say haha

again, not so much. If it fits in the groove it's going to seal. You could put in hot glue and it would seal (until it's melting temp was reached... and it's viscus properties dropped like a rock).

it just seems like string and rtv is going to wear out a lot faster than anything else

Why?

The heat cycling will only affect the RTV, and even that is made to be heat cycled.

It's no worse than rubber/silicon based seals. There's no "moving" parts involved, and once the seal has been made it's not going to suddenly be "unmade" unless something happens to the groove, ie: casting falls away, the engine is torn down, pressurized steam by-passes the groove and eats the seal, etc.

The main purpose of the seals is just to contain the coolant and keep it out of the combustion chamber. Pressure from the combustion process should be kept to a minimum on the seal itself--this provided by the geometry of the seal groove itself.

Ive got stright rtv on my t-stat housing and my water pump. Been there for bout 76000 miles just fine. I'd trust rtv, as long as there is enough to fill the groove good, thats where the string would come into play i believe. Sounds like a quick, im broke as hell, rebuild to me. I wouldnt trust it in a race or high hp car but a dd sure.