Ok. Thank you for clarifying your position with regard to son and dad relationship.
The key consideration would be whether there is a genuine relationship with his British child for your husband to be granted a visa to remain in the UK under the category of a parent of a child in the UK. If your relationship is broken down and you no longer can meet the financial requirements under Appendix FM, it is unlikely that your husband is able to remain in the UK as your spouse. Everything else with regard to your debt and the fact he hasn't worked in the UK is irrelevant. Your don't have to be divorced, as the key issue is whether there is a genuine and subsisting relationship and if there isn't divorced or not, it is unlikely that your husband is able to remain in the UK under a spousal visa.