In this paper, we quantify integrity for a GNSS-PPP system when augmented with mega-constellation satellites (GNSS-MC). The geometric diversity provided by signals from fast-moving LEO satellites is exploited for rapid estimation of floating valued cycle ambiguities. Further, the improved redundancy provided by mega-constellation satellite signals in addition to GNSS enable efficient fault detection using carrier phase Advanced Receiver Autonomous Integrity Monitoring (ARAIM). The proposed framework assumes that mega-constellation (MC) satellite orbit and clock determination is based on their spaceborne GNSS receivers. We quantify the impact on integrity of GNSS faults, which not only affect the potential users on earth, but also the spaceborne MC receiver data. Given that GNSS faults can cascade to constellation-wide MC faults, this work determines the conditions where GNSS-MC improves integrity, and quantifies this improvement as compared to GNSS only.