Thanks for your patience. First of all he cannot sue you for unfair dismissal because he needs 2 years’ service with you to be able to do so. Those with less than 2 years service cannot claim for unfair dismissal unless the dismissal was due to discriminatory reasons, such as their gender, race, age, religion, etc. This does not appear to be the case here so there is unlikely to be grounds under which an unfair dismissal can be claimed.
He could potentially try and pursue you for the notice period but if you can show that his actions were indeed gross misconduct he will not succeed with that claim either.
As to whether you can sue him for correcting the work he deleted that would be possible depending on a few factors. For example, were they under specific instructions not to delete the code and did so with full knowledge of the repercussions it would cause the company? Were the costs in recovering the work reasonable and could these have been mitigated in any way – for example is that the absolute reasonable minimum you could have spent on recovering the work or did you spend more than necessary. These are all things a court would look at when considering a potential claim. It is certainly possible to sue him for the damages caused and the losses incurred, it is just that you may not necessarily recover the full amount, rather a proportion of it.
This is your basic legal position. I have more detailed advice for you in terms of the steps you need to follow to take this matter further, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you