Read through the quote included in
this post.
BIA response to query regarding qualifying period and absences (Extract from linked post)
"The total duration of absences abroad that are allowed in the 5 year qualifying period have remained the same as under the 4 year qualifying period. That is the total duration of absences abroad that are allowed in the 5 year qualifying period for ILR for Work Permit holders is 6 months. Please note that absences should not exceed 3 months at a time and should not amount to more than 6 months in all".
A letter from employer will help as any period spent outside UK on official assignment will not be considered as break in residency.
In your case, compassionate reasons should also be enough (hopefully) for the case worker to apply his / her discretion (which he is allowed to do). But a letter from employer makes it easier for you and for the caseworker too !!
Hope this helps.
regards