The heading of the plane at ISBIX is 186T. The apparent choices (made without pilot input) would be TT, TH, MH, (others?). Most pilot responses seem to be that it defaults to "heading". But this begs the question of how are winds treated? Is there any compensation for cross-winds?
When you pass the last waypoint on the plan, or a route discontinuity is next, LNAV maintains the current heading (M or T). It’s a heading so the ground track will vary according to the sum of the aeroplane TAS+heading and the wind vector being experienced, so unlikely to be a straight line over more than a short distance. If you’re flying a MH, then the TT will change as the magnetic variation changes, driven by the FMC database.
Some people answer that they use True Track, over oceanic regions either to check their path or to navigate. Since most We are taling about a 777 in 2014 and one imagines that all navigation is done through the FMC. So, does the pilot switch from MH to TT once clear of local ATC.
Depends on airline SOP. We stay in MH (although the FMC will automatically switch to TH in polar regions); others may go to true in all oceanic airspace, YMMV.