tartine bread without dutch oven (inverted mixing bowl on top of heavy skillet)?
Overall, you should be fine. The purpose of the dutch oven is trapping moisture and, to some extent, coralling the dough. 

Keep the following in mind:


Make sure your bowl can handle the heat - high heat might cause it to warp. To some extent, this is fine, but if the gaps at the bottom get too big, you won't trap the steam the way you want. But some loss is fine, the bread needs to "dry" a bit.
Your dough should not be too runny, otherwise it might stick to the bowl and make removal somewhat messy (unlike in a dutch oven, it would be difficult to use parchment paper to keep the sides from sticking). So make sure, the bowl is big enough and the loaf well shaped.
Unlike the dutch oven lid, the inverted bowl has no handle and is likely to slip when you try to lift it, please be extra careful not to burn yourself!
If you put a cool bowl over the bread, you might get some condensation you wouldn't get from a pre-heated dutch oven lid. Drops of moisture may leave traces on the crust, but that won't affect the quality of the bread. With a nice dome-shaped bowl, this effect should be minimal.


----Edit----
There are a couple of ways how to bake tartine bread w/o a dutch oven. For one example from our seasoned advice, see here.