leitaði lífs. Gwyn Jones has "The first thing Sam did was to look
for life", which would have been my guess too.

hvat leika er. GJ "what game was afoot". Zoega quotes this and a
similar idiom: 'segja hvat í leikum er', both defined "say what the
game is, what is the matter".

þá er umskipti á orðit með þeim. GJ "by this time the battle was
over". The outcome or result of the battle had been decided. Cf.
the second definition in Fritzner: 'umskipti' "outcome of a clash
between enemies".

(1) umskipti hafa nú orðit ok mun Vandill drepinn, ok leggjum á
flótta
"the fight's decided now and Vandil will have been slain; we'd
better flee"

(2) þá mun hér verða skjótt umskipti at ek mun láta drepa þik
"then it won't take long to decide the outcome of this; I'm going to
kill you"

(3) berjask til umskiptis
"fight to a conclusion"

var þat trúliga gört. GJ "but the job had been thoroughly done".
From the context, and maybe from the way the next sentence follows
on with no adversative conjunction, I assumed it refers to the
killing rather than the examination.