[Just saying,
http://csep10.phys.utk.edu/astr161/lect/solarsys/nebular.html
This would seem to imply that the nebulous hypothesis is more philosophical than scientific. Not a bad effort for the time, but probably insufficient these days.
As for the steady state theory of cosmology, it doesn't seem to have held up well after the discovery of the background radiation predicted by the Big Bang theory. I'm not sure what this has to do with the conversation at hand, but it seems to be inconsistent with contemporary measurements.
And as for heat death, it seems to be a possibility. We don't know if the universe will continue to expand into infinity, in which case heat death is a likely end. If, however, the universe eventually re contracts, due to dark matter, etc. then heat death will not occur. We don't really know yet. Stephen Hawking's "A Brief History of Time" gives both scenarios. I wish I understood it better.
DF