There is no Federal requirement to reimburse employees for work-related expenses
Unless the effect of those expenses pushes the wages below the Federal minimum, there is no statutory or common law requirement for the employer to reimburse.
Contract law
Notwithstanding the above, the employer and employee can contract that such expenses will be reimbursed, either one-off or on an ongoing basis. This might be a term of the employment contract or a seperate collateral contract.
How and when the reimbursement were to occur would be governed by the terms of the contract.
State and local law
Currently, 11 states, the District of Columbia, and Seattle, Washington, have laws about reimbursing employees for necessary work-related expenses.
Fortunately for you, one of those states is new-hampshire:
An employee who incurs expenses in connection with his or her employment and at the request of the employer, except those expenses normally borne by the employee as a precondition of employment, which are not paid for by wages, cash advance, or other means from the employer, shall be reimbursed for the payment of the expenses within 30 days of the presentation by the employee of proof of payment.
You can ask “the department” to enforce the law or take action in any court of competent jurisdiction. Legally you cannot be fired for reporting a violation of the law or in retaliation for enforcing your rights but doing either is likely to tick off your employer. By the way, the state might send him to jail for not paying you.
If you leave, you are still owed the money.
If the company goes bankrupt, your entitlement will rank alongside other unsecured creditors so, no, you probably won’t get paid, or, if you do, it will be cents in the dollar 5 years from now.