According to the Nature paper (last section of http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html http://www.nature.com/nature/journal/v542/n

According to the Nature paper (last section of http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html http://www.nature.com/nature/journal/v542/n7642/full/nature2...) -- We computed [via n-body and other simulations] that TRAPPIST-1 has a 25% chance of suffering an instability over 1 Myr, and an 8.1% chance of surviving for 1 billion years (Gyr), in line with our n-body integrations. And, further, However, [these lifetimes] do not take into account the proximity of the planets to their host star and the resulting strong tidal effects that might act to stabilize the system. ... The masses and exact eccentricities of the planets remain uncertain, and our results make it likely that only a very small number of orbital configurations lead to stable configurations. ... The system clearly exists, and it is unlikely that we are observing it just before its catastrophic disruption, so it is probably stable over a long timescale. These facts and the results of our dynamical simulations indicate that, given enough data, the very existence of the system should bring strong constraints on its components’ properties...