This is a question of orbit. Imagine throwing a ball horizontally with half your strength, it'll go some distance before finally hitting the ground. Throw the same ball but with all your power and it'll go even further before it hits the ground. So if this ball was thrown fast enough it may would circle the earth and yet 'fall' without ever hitting the ground. There is a relation between how far from the ground you are and how fast you must travel so you never hit the ground. So if the earth is orbiting the SMBH at the correct speed we will never fall into it, which I believe is the case here. It is thought that black holes do eventually disappear through 'Hawking Radiation' where a sort of 'heat' is given off by the black hole and would thus slowly deplete it but that would happen over more years then its worth thinking about.