Thanks, Michael.

I`ve already done it (by network with using 4 edges patches) but your last method is a lot faster :)

So process of rebuilding flat faces based on boundary edges is:

3 or 4 edges - select edges and click network button
more than 4 edges (flat) - select edges, click planar button, fire script: "ShrinkTrimmedSrf" (why there is no button for that?)
more than 4 edges (curved edges - flat face) - select longest curved edge and extrude it, trim rest and cut out

Thank you very much.