If bitcoin is splitted after August,and someone send the btc to some other btc address during this period, will those in trasit btc lost for ever?
Just to be safe I'd recommend holding your bitcoins till atleast 1 week after the event. If there would be any split it could take a couple weeks (I was said that it took 2 weeks for ethereum to split). Also makes sure you don't store your coins on an exhcange or a 3rd party wallet. Always make sure you have your private keys.