Just as a quick addition to what scvvuuren said, once your maintenance expires. SolarWinds does not guaranteed your eligibility to renew and it is possible you might need to repurchase an out of maintenance upgrade. Also, maintenance pricing is not determined by a percentage of the new license MSRP pricing, but by the value of the updates provided.
I would reach out to your renewal representative (or maintenance@solarwinds.com) and let them know you are interested in renewing, but you will pass (or are past) your expiration date.
Hope that helps!