It is now downloading blockchain again from beginning ?
I tried to restore a good chunk of the block file to speed it up and it failed, so yes, it is going to have to slave its way trough the entire block chain.
How about incising that retry to at least few days? It can try frequently for the first hour and then it can try like once pen hour.
Well if your server is down several days, you should be confirming the payments manually anyway.
Could maybe increase the delay to a few hours.
Also is there option that BitPing requires specific reply from my server? Something like 'OK' ?
No, any 200 resp will do.
I plan to use it for exchange and I think those are options that I need to make it reliable.
Then you should probaly run a local service, instead of depending on an external service.