Is it possible to have gingivitis ==> bone loss?

Yes: If not properly treated gingival inflammation (gingivitis) can progress to periodontitis (bone loss).

Indirectly, Yes: Nearly everyone has gingivitis. If you have any plaque on your teeth anywhere, you'll have some associated gingivitis. However, this is reversible with a professional "cleaning" & excellent oral hygiene. If it's left untreated, however, it very often progresses to "periodontitis, " which leads to irreversible bone loss. So, gingivitis by itself does not destroy bone, but it can get worse over time.

Yes: If the gingivitis becomes severe it can lead to bone loss around the teeth. However, gingivitis is easily treated by your dentist.