It looks like in new versions of Asterisk silencedetecthangup is no more supported.
Problem - if some of SIP clients die - call persists. If both clients die - call can persist until Asterisk restart.
As I read, silencedetecthangup is designed just for this - if there is absolute silence for more then timeout, then call should hangup.
What I did was - 2 SIP clients connected to Kamailio make call through Asterisk.
Then I dropped connection for one client and then for other - and call persists.
I am curious if silencedetecthangup is dropped, or just I am not using it properly.
rtptimeout - works exactly as I need.