Will the COVID-19 visa extensions be prolonged past March 30th, and what documents are required for Immigration?

You’ll need this stuff. Not all offices have the same requirements so it may be slightly different depending on which of the 70+ offices you use.

A copy of your passport data page (signed),

A passport photo,

Proof of filing a TM30,

A copy of your departure card (TM6) (signed)

A copy of your latest entry stamp (signed)

A copy of any previous Covid extension stamps (signed) (Phuket requires this other offices may not)

In Phuket they require the copies to be in portrait not landscape. This means the top of your passport aligns along the shorter side of the A4.

(Other offices may not be as pedantic)

A filled out TM7 (application form for extensions) - the form doesn’t have a space for your email or phone number but just write it on the back (page 2).

A filled out STM2 (acknowledgement that you understand the rules for overstaying)

A filled out “I don’t want to leave because of Covid form” - I have no idea if it has an official name or number.

And 1,900 baht.

The forms are available at your local office. Most have places on site or nearby that can do the copies and photos.

you need to go in with passport and TM 30 and 1900 baht, go to copy office in the back and fill out 4 pages of forms, make copies, submit.

The Emergency Decree was already extended an additional two months.

Nobody knows for sure at this point. Although it is likely to be extended. If so, probably last minute on short notice, as it has been before. The rest of your question would seem to consist of a logical error, cause if it is NOT extended, no need to bring documents to immigration 😉