Long term contract with employer

The employer decided to conclude a contract with me and my colleague for a period of 2-3 years, motivating this by the fact that he invests money in our training and certification (training in courses, exams, trips to conferences) and, of course, does not want to stay with than if we suddenly want to topple down having gained knowledge and experience at his expense. We are engaged in 1C programming and implementation, without passing the 1C exam, the Specialist is especially nowhere, and restrictions are imposed on the partner company if there are not at least two people with such a certificate in the state. And hiring ready-made specialists is much more expensive than growing your own.

They promise a salary (the average for a programmer in our city at the moment) + bonuses if you make a profit for the office more than a certain amount.

The working conditions are good, but the long term of the contract and the poor state of the economy recently have been scary.

I want to ask the community a question - what can be the pitfalls and what should you pay attention to when signing up, so as not to end up with a penny in a year in the event of a depreciation of the ruble or other reasons?