Sustaining Excellence in Medicaid Act of 2019 This bill extends several health care programs and requirements and revises certain Medicare drug payment methodologies. (Sec. 2) The bill temporarily extends the Medicaid demonstration program for certified community behavioral health clinics. (Sec. 3) The bill also temporarily extends the applicability of Medicaid eligibility criteria that protect against spousal impoverishment for recipients of home- and community-based services. (Sec. 4) The bill increases appropriations for FY2019 for the Money Follows the Person Rebalancing Demonstration Program. (Under this program, the Centers for Medicare & Medicaid Services (CMS) may award grants to state Medicaid programs to assist states in increasing the use of home and community care for long-term care and decreasing the use of institutional care.) (Sec. 5) Additionally, the bill extends the Family-to-Family Health Information Centers Program, which is administered by the Health Resources and Services Administration. The program awards grants to family-run organizations to support the provision of information and peer support to families of children with special health care needs. (Sec. 6) Finally, the bill provides statutory authority for a Medicare payment methodology that applies an add-on payment of up to 3% for new drugs or biologics (furnished on or after January 1, 2019) when the average sales price is unavailable and payment is instead based on the wholesale acquisition cost (WAC). (Effective January 1, 2019, the CMS reduced the WAC add-on payment in such situations from 6% to 3%.)