Is there some limitation to the growth/duration of a Vortex of Doom that I've overlooked? RAW suggests that the majority of these grow until they consume the world they were created on. I ran it thru 20 rolls of a RNG several times just to double check. YMMV, my figures after 20 rounds were 25% collapsed and the rest growing steadily.

Yep. Vortex of Doom is basicly a new Eye of Terror in the making, as it has a higher chance of growing infinitely. Not really worth any risk.

Unless you are a chaos librarian then wooohooo best power ever.

In character I would seriously kill any space marine (chaos or otherwise) who used that power for any reason what-so-ever. No matter what else ever happened that marine would need to die.