First of all, let's talk about the reason why you didn't reply to the message. Is it because you ran away and deliberately didn't return the message, or because you didn't see it or for other reasons, you accidentally didn't return the message? If you deliberately don't reply to the news, no matter whether it causes losses to the company, you have nothing to say when you are criticized, but you can only admit it. Although work and private life should be separated, off-duty time should be entirely their own time, but how many people in today's society can really do it? As long as you still need this job, just admit it! If it is unintentional, accept criticism with an open mind. Then, if your reasons are justified and sufficient, reveal them intentionally or unintentionally, and let the other person know that you still love your job and work hard. This time, you have to do it
If it's not enough, you'd better not say too much, accept criticism with peace of mind and pay attention next time. The premise remains, if you need this job. Then see what the other party sent you. If it is work-related news, you didn't reply, which brought losses to the company, or slowed down the progress of the project, and so on. Then you should be criticized.
Although your private time is your own, as long as you are an employee of the company, you should be responsible for your work. As long as it is not a force majeure or a major accident, you should not deliberately not reply to the message. If it's not intentional, accept criticism. After all, what you see in the workplace is the result, not the process. If it's not work-related, but a private letter, it's his fault that he criticizes you. You only have a working relationship with the company leader, not a personal relationship. This kind of private letter is not usually sent to you. If he still shamelessly criticizes you, you can ignore it or even re-examine it. Is it necessary to follow this leader and have a future?
Finally, see if you want to continue working in this company. If you don't need this job anymore, as long as it doesn't cause serious property losses to the company and won't make you bear any legal responsibilities, then you don't need to take care of it, or you just walk away. If you still need it, there will inevitably be moments when you have to swallow it.