"Fall of the Camarilla: Fall of the is a temporary effect. Once the
card is out of play (by ousting the controller, for instance), the
underlying sect of the vampires is again 'active'." [LSJ 20040519]"

"Each vampire's sect is given in its card text, and that may override
the default sect of that vampire's clan (see the lists in the
following sections). If a vampire changes clans (by means of a Clan
Impersonation card, for example) to a clan that belongs to a different
sect, he changes sects as well." Online Rulebook, section 10

QUESTION #1:

Fall of the Sabbat is in play.  Lucretia (Camarilla Nosferatu) plays
“Clan Impersonation” to become a Lasombra.  Later, Fall of the Sabbat
is burned.  What sect is Lucretia now:

GUESS #1:  Since “there is no Sabbat”, the default Lasombra sect is
considered “Independent” at the point this Clan Impersonation is
played & the Section 10 rule triggered.  Lucretia therefore becomes
Independent.  Later, when “Fall of the Sabbat” is burned, Lucretia
remains Independent, since no mechanism exists for automatically
altering the sect of individual vampires when the clan itself switches
sects (see Giovanni Acceptance, et al.).

GUESS #2:  “Fall of the Sabbat” doesn’t change the default sect of
clans, but merely the sect of vampires.  Therefore, when Lucretia
plays “Clan Impersonation” and triggers rule 10, her “underlying sect”
is permanently changed to Sabbat.  However, because of the ongoing
effects of “Fall of the Sabbat”, she will be considered independent as
long as Fall of the Sabbat remains in play, and become Sabbat when it
burns.

GUESS #3:  “Fall of the Sabbat” does not change the default sect of
clans, but merely the sect of vampires.  Therefore, when Lucretia
plays “Clan Impersonation”, the section 10 rule dictates that she
should become Sabbat.  However, with Fall of the Sabbat in play, this
rule is over-ridden, and the change is prevented from occurring.   She
becomes Lasombra, but her sect remains Camarilla.  She will continue
to be a Camarilla Lasombra, even when Fall of the Sabbat is burned.

QUESTION #2:  As above, except, instead of playing Clan Impersonation
and triggering the Section 10 rule, Lucretia becomes Sabbat via "Into
the Fire".  Does she become Independent (per the reasoning in Guess #2
above) or remain Camarilla (per the reasoning in Guess #3 above).