This article is from the rec.arts.sf.written FAQ, by Evelyn C. Leeper firstname.lastname@example.org with numerous contributions by others.
"How exactly is the meeting with the riselka at the end of Guy Gavriel
Kay's TIGANA supposed to apply to the three characters who meet her and
is there anything in the book which offers suggestions or is it just
supposed to leave readers guessing?"
The collective opinion of rec.arts.sf.written is that it is meant to
leave the book deliberately open-ended, there being no indications in
the book itself, beyond the obvious balance of probabilities.
From an interview with Kay by Andrew Adams (email@example.com):
Q: The end of Tigana with three men seeing a riselka suggests
to some a hook for a sequel, to others merely an indication
that "life goes on...". Do you have any plans to return to
GGK: The second theory is entirely correct. To put it another way,
I wanted the sense that this whole very long story is NOT the
whole story of these peoples' lives. No sequel was planned or
hinted at. I think most thoughtful readers picked up on the
point, but there have been an awful lot who have been waiting
for the next volume. This depresses me, actually.
And "Riselka" is indeed spelt "riselka," despite many creative attempts
towards alternative spellings. It presumably comes from the
Slavonic "rusalka" -- a female water spirit.
[Provided by Mike Arnatov [firstname.lastname@example.org].]