Your extension of stay will be made invalid as soon as you leave. You have to cancel that and then under normal circumstances you would apply for a covid19 extension with embassy letter (Immigration still accepting them if you can get it).
If the law passes (which it has not today yet), then you shouldn’t have to do anything (maybe cancel).
Non immigrant visas extensions are extended as normal if you still meet the conditions of the extension.
However if they are expiring due to you not meeting requirements of it or you don’t meet the requirements anymore You can apply for the emergency extension as long as you get the letter from your embassy.
If you are on extensions you must cancel the extension first.
You can apply for an emergency visa after receiving paperwork from your embassy AND also cancelling any extensions if you don’t meet the requirements of the extension.