Jamieson, Fausset and Brown on Hebrews 1:11

11. They--The earth and the heavens in their present state and form "shall perish" (He 12:26, 27; 2Pe 3:13). "Perish" does not mean annihilation; just as it did not mean so in the case of "the world that being overflowed with water, perished" under Noah (2Pe 3:6). The covenant of the possession of the earth was renewed with Noah and his seed on the renovated earth. So it shall be after the perishing by fire (2Pe 3:12, 13).

remainest--through (so the Greek) all changes.

as ... a garment--(Is 51:6).