23 March 2022:
Matt Robison of Lullabot has written a very well-balanced analysis of the choices facing owners of Drupal 7 sites, after Drupal 7 reaches end of life (currently scheduled for November 1 2023).
He covers the advantages, and possible steep learning curve, of moving to Drupal 8/9. For many that is the best option.
He also conveys that moving across to Backdrop CMS may be the appropriate choice for many other site owners.
He also mentions the possibilities of moving out of the Drupal-Sphere completely.
Over 50% of Drupal sites are still on Drupal 7. The numbers show that a lot of site owners are unaware of the need to move off Drupal 7, or, if aware, are reluctant to put in the time and resources to do the work.
Stanford University recently upgraded from Drupal 7 to Backdrop CMS for both their off-campus learning program (solo.stanford.edu) and internal research funding program (seedfunding.stanford.edu), two sites that had extensive custom code. They estimated that upgrading to Backdrop was one-fifth the cost of rewriting their code for Drupal 9 — the equivalent of $400,000 in savings for their project. [so $100,000 instead of $500,000]
You have many options available and an extra year to decide and plan for one of those options. The best choice depends on your team's experience, how much business logic you have baked into Drupal 7, and your potential budget.