Hi, I am gonna to buy routeros license. I want to use it on alix boards(pc engines) and save it on compact flash, but I am little worry about destroying compact flash with a lot of writes.
What do you think?

In my opinion there is no need to worry about wearing out the flash. On most RouterBoards the RouterOS is stored in the on-board NAND flash and working without a problem.

you dont get the point what I mean. Alix is x86 device where you can connect compact flash card, on this compact flash card you install routeros.
http://pcengines.ch/

He did get what you mean, and his answer is correct. Yes, there is no problem to use RouterOS on a Compact Flash.