Say if there are two static route to isp and if one fails how does the other link send the remaining data & even if the data is continued from very much same point of failure. Will the assembly of the packets will be a a success?
The problem with static routes is that the router doesn't know if the link fails. So the router will continue to forward packets out the failed link, and they will be lost.
If there are two equal routes in the routing table, then the router will alternate paths and you'll lose every other packet.
It's up to the end host to determine that data is lost and either timeout or request retransmission.