Will the Weekend quota be granted to me permanently if I sign up during the promotion period?

Yes, you will get to enjoy the Weekend quota for life, as long as you remain on the rate plan and sign up during the promotion period.
 

Example: You signed up for Digi Postpaid 150 Family during the promotion period. You will get to enjoy 30GB All Day quota and 30GB Weekend quota every month for life, as long as you stay on the same rate plan. If you change your rate plan or terminate your line, the offer will no longer be applicable.