I need some eye bleach after looking at that addon's code.
Anyway, Lua does have regular expressions, but it calls them "patterns". If the tooltip for the Combustion debuff shows the correct damage amount, then you could use tooltip scanning to extract that amount. This involves creating a custom hidden tooltip, though, so it may be more appropriate for a full plugin than for a simple tag, especially if you need to keep track of other details like talents or glyphs. The addon you linked looks at both of those things, and more, but as I haven't played a mage since 2005 or so, I don't really know how much of that is relevant for just Combustion.