Hello.
what exactly happens on level of application in virtualized VM when there is big latency vLockstep interval and suddently primary crash? How this execution lag is replayed on secondary when primary is suddently down? Is it like even there is big vLockstep execution lag secondary host got logs locally everytime prepared for execution but it is waiting locally on secondary for real execution of logs on its CPU, is it like that?
Have you seen the "[The Design and Evaluation of a Practical System for Fault-Tolerant Virtual Machines|http://www.vmware.com/files/pdf/partners/academic/fttech.pdf]" document? It explains the entire process in detail far greater than I will attempt to summarize in a sentence or two. 
Good Luck!
Hello,
great document! 
Maybe this is that important part:
"If the primary VM fails, the backup VM should similarly go live, but the process is
a bit more complex. Because of its lag in execution, the backup VM will likely have a number
of log entries that it has received and acknowledged, but have not yet been consumed because
the backup VM hasn’t reached the appropriate point in its execution yet. The backup VM
must continue replaying its execution from the log entries until it has consumed the last
log entry. At that point, the backup VM will stop replaying mode and start executing as a
normal VM."
"Since it is no longer a backup VM, the new primary VM will now
produce output to the external world when the guest OS does output operations. During
the transition to normal mode, there may be some device-specific operations needed to allow
this output to occur properly. In particular, for the purposes of networking, VMware FT
automatically advertises the MAC address of the new primary VM on the network, so that
physical network switches will know on what server the new primary VM is located. In
addition, the newly promoted primary VM may need to reissue some disk IOs "