Long term contract with employer

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

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

Working conditions are good, but the long term contract and the poor state of the economy have been frightening lately.
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I would like to ask the community a question - what pitfalls can there be and what should I pay attention to when signing, in order not to be in a year with a penny salary in the event of a ruble devaluation or other reasons?