one prior conviction isn't necessarily a block to probation, however it will be taken into consideration as will the alleged assault, her injuries and their relationship. As for a reduction, that is unlikely given the injuries you note however it is not impossible. I do know that Lubbock is very strict on domestic violence crimes so it will be an uphill battle. He needs an attorney immediately.
Although my intent in answering this question is to aid you in the legal process, my answer does not establish an attorney-client relationship in any way. You should seek the advice and counsel of a qualified attorney in your community to evaluate your legal needs and to advise you. No Attorney-Client Relationship is created without the specific intent of both parties.
Since he is in the rehab, he should try to finish. Then, he needs to be prepared to turn himself in as soon as he gets out of the rehab.
A person with prior felony convictions can get deferred adjudication probation for eligible offenses, and this charge is eligible. Whether or not the State would consider offering it to him is a completely different question. It sounds like a pretty bad assault. They could reduce it to a misdemeanor but I really doubt it with the facts you have presented.
The fact that he was subsequently diagnosed with bi-polar and went through treatment may well help sway the prosecutor to give him deferred. The complainant will have a lot of input on this.
Yes, she can record their conversations. In Texas, only one party to the conversation needs to consent to being recorded - and if she is recording it then she is obviously consenting.
He needs a lawyer.
Although I have answered the question to try to help you, you should consult with a lawyer in your area in person on the matter. In addition, my answer does not establish an attorney-client relationship between us.