Yes the contents of the flash memory will "stay there" until you decide to erase them.
Many uCs with on-chip flash memory use it as a code memory.
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From http://webopedia.internet.com/Top_category.html
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Flash is a special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their BIOS stored on a flash memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized.