Given that you had a 100% repayment plan, it's not clear that reopening the case would benefit you -- it could be that this new debt would not have changed your plan from being 100% repayment. Your lawyer has the details and we do not, so you need to discuss the facts and your lawyer's strategy with your lawyer.

Your present financial situation is not relevant to how the bankruptcy court would have treated the tax debt, had it been included in your bankruptcy.