Tier 4 Visa Submitted Application - Queries

Hi all! I was hoping someone might be able to give me advice on the questions below (thanks in advance and sorry for the long post).

General details about my application:
Type: Non-Priority Tier 4 Visa (Postgraduate)
Online submission submitted: 18 August 20
VFS centre: Kuala Lumpur, Malaysia
Biometrics submission: 25 August 20
(Awaiting decision as of today)

Previous Immigration Details:
I previously held a Tier 4 visa (undergraduate), applied for an EEA Partner visa but gave this visa up last year, notified the Marriage Curtailment Team and sent them my flight details leaving the UK (this was also sent to my current university).

Post-Application Details:
1. My university emailed me on September 9th notifying me that my CAS has been marked as 'used'.
2. As of today, it's been 15 working days since the application and I've not received any form of communication from the application/decision making centre (nothing notifying application submitted, received etc).
3. I rang UKVI yesterday inquiring about the application status and was told that it's still being processed and a query will be sent to the decision making centre but I should expect their reply within 20 working days.

Questions:
1. Could my application be deferred without being communicated with?
2. Is the decision making centre obliged to have a decision made within the 15 working days timeframe I was told?
3. Will I receive an email from UKVI that a decision has been made?
4. Is the passport held within the local VFS centre or sent to the Home Office in UK?

Apologies for the long post - freaking out a little here because my flight is in a few days.

TLDR.

I advise you check all this with the university that is sponsoring your Tier 4 visa. They have a "hotline" to the UK Home Office.

Alright thanks!