There are two questions where I would want to know a little bit more:
Currently, it is not possible. It might be possible in the future to ask a third party to watch for the incoming payment.
Yes, due to many factors. Lightning Network implementations are still in beta and might contain critical bugs which could be used to steal funds locked up in channels. Keep in mind that if you won't keep your node online 24/7, someone can attempt to cheat you by broadcasting an old state of your channel. An online node would normally broadcast a penalty transaction.
Here an interesting addition is if there is a "standard" timeout/lock time for the Lightning "penalty transaction" - to know how often you should be online to avoid being cheated. I've currently no Lightning node running (I tested Eclair some weeks ago but it's now outdated, so I can't answer that question myself.) Normally, you should be able to set the timeout you want, but what are the chances you will find a route or a partner to open a channel with?