The old composer has gone nowhere. It’s still available via the toolbar toggle. You do not have to enable the rich editor setting if you do not want to, and we have no intentions of removing the Markdown only mode or forcing anyone into the rich text composer.
I won’t argue that the rich editor has zero bugs — no software does — but we have tested it extensively for months, and we will continue to improve it going forward.
For the time being I will close this topic but please continue to share bugs / feature requests as you identify areas where the new composer is lacking.