Four Kinds Of Timelines

In Poul Anderson's works, "time travel" occurs in diverse timelines where, e.g.:

(i) many space-time vehicles continually appear from, or disappear into, actual or potential pasts or futures;

(ii) a few space-time vehicles, expending immense amounts of energy, move across Earth's surface while also moving backwards or forwards in time;

(iii) a few mutants move backwards or forwards in time without vehicles;

(iv) two warring groups move backwards or forwards along corridors that have been rotated onto the temporal axis.

It is as if the author has systematically considered every possibility:

(i) many vehicles;
(ii) few vehicles;
(iii) no vehicles;
(iv) corridors instead of vehicles.

In (i), the vehicles do not move but merely disappear and reappear.
In (ii), the vehicles and their occupants, described as "moving," really only age/endure/durate at a reduced rate.
In (iii), the mutants do likewise.
In (iv), the corridor-users really do move along the temporal dimension of the external universe.

In (i), time travelers can "change the past"/violate causality.
In (iii) and (iv), they cannot.
(ii) is ambiguous. The dying futurian, Sahir, asks Duncan Reid to contact other time travelers who will arrive a year hence and says:

"'They'll come through time, to this day, bring help, surely -'"
-Poul Anderson, The Dancer From Atlantis (London, 1977), Chapter Four, p. 33.

Does he think that there might be a divergent timeline in which he is rescued?