firstly, the issue of whether they are Bengali is still officially undetermined and secondly, EVEN if they ethnically are, is the State of Bangladesh responsible for the fate of all Bengalis, whether they have been residing in Assam, West Bengal, Arakan, Tripura etc. for decades? Should they have an open door policy where every person who has Bengali heritage can waltz in and claim Bangladesh citizenship? I don't think so.
My view is simple. International pressure should be exerted on Myanmar first and foremost to end such atrocities. Whether they are committed against a group they consider as being part of their citizenry or not - that is a separate issue - but what they are doing amounts to ethnic cleansing at best and genocide at worst. Whether Bangladesh or Thailand is willing to grant refugee status to them is a secondary issue and the decision to grant it should be done under the respective country's immigration/asylum laws and international conventions such as the Refugee Convention 1951, not some vague concept of citizenship and belonging. Given the horrific situation now, on that, and that ground alone, Bangladesh should consider granting them refugee status.
Unfortunately, the Ramu calamity will not help the Rohingya cause and will give the Government further reason to take no action on this issue, as it has been strongly alleged in the media that it was some members of their community in Chittagong that were partially responsible for destroying Buddhist religious and holy sites.