No matter how bad a person is even if he sims avoda zara it’s never too late to do teshuva. King menashe and a chef sinned the worst FOR 30 YEARS AND at the end of their life did teshuva WHOLEHEARTEDLY and it was accepted because they really meant it.
Klal yisroel today as a nation can still do teshuva and stop the tzaros from continuing if they WHOLEHEARTEDLY do teshuva together as a nation begging Hashem forgiveness and return to Achdus and ahavas yisroel
That may be in a personal sense ,However in a public sense it’s false
The Yidden in the Midbar had die ,and were refused any possibility of teshuva
There was a famous story from Europe of a great maskil who was told when he came to do teshuva that the only way to undo the impact of his effects would be for him to publicly abandon his Judaism altogether