Could the crew of XL Airways Germany Flight 888T not hear important chimes, due to the stall warning?
When the stall has developed the aircraft is no longer in normal control law for any axis (see more in FCTM at OP-020. P 14):

As soon as the aircraft is outside the flight envelope, the control laws transition to abnormal attitude which is the combination of:


Roll direct
Pitch alternate
Yaw alternate.


This is something between alternate and direct, and is intended to allow the crew to recover from the abnormal attitude and reenter the flight envelope without being prevented by some protections.

A stall (an excessive angle of attack) is one of the conditions to switch to the abnormal attitude laws. You may read this article too, while on a simulation site, it is very well written. There is also a presentation on SKYbrary at Eurocontrol.



When the stall warning aural warning is active (voiced "Stall" and cricket), the crew is expected to know they are in abnormal law.

Reconfiguration in abnormal attitude law is indicated by different clues on the PFD (e.g. $\alpha$ prot and $\alpha$ max indication removed from the speed strip, and green = replaced by amber crosses).


Source


Source

and the master warnings are activated. The aural alert is a single chime, (level 2 failure confirmed in this report, page 25). The reconfiguration is also indicated on the ECAM, but the indication can be moved towards the bottom of the list if messages with higher priority arrive.

The law is reconfigured as direct when the landing gears are lowered.



Regarding the aural warnings associated with stall and law reconfiguration, they are audible at the same time, or are intercalated, but none cancels the other, as it was heard for AF447 and reported in this article (C-chord is the single chime):


  In sequence the alarms were sounding PULL UP, C-chord, STALL, C-chord,
  PULL UP, PRIORITY RIGHT.