Dear Gopal,
I believe there are a few things that need to be understood and better implemented in a career stuck in this career quagmire:
1. Whatever impression an organization may tend to convey, knowledge related to HRM is no rocket science. It may be difficult to digest this after having spent so much time in this field and that too post a 'change' operation. Having said this, it leaves a person more vulnerable to attacks resulting out of petty politics, undesirable expectations related to employee 'loyalty' or so-called stability, greater dependence on views and opinions of elements in your 360 degree 'professional' space & illegitmate interests of your legitimate or illegitimate stakeholders and other actors.
In retrospect, it is always easy to suggest solutions like you should have refrained from 'interfering' in corruption orgy of the alleged sexual harrassment 'victim' & her vendors or that you may have been more tactful in taking up this issue, etc. However, the fact remains that whatever contributions or in some cases sacrifices one may make towards 'his or her' organization, the relationship of an employee and employer would always be like that of two adults who focus on win-win outcomes, who may have selfish interests and who may not always act rationally forget recognizing your contributions. So it would be better if you make it a point to remember that if you are being sincere towards an organization, it may not be reciprocated by a similar treatment.
2. Now if you agree to the view or observations in point one, then the second thing you may want to think about is that whether or not you really want to stay in HR function. Some people may consider change of function as a taboo or an act of 'professional blasphemy'. But the issue does not lose its significance despite the best managed attacks by professionals ailing from 'entrepreneurial poverty'(often consciously or unconsciously taught & fed on so-called best practices in industries and having lost the vision of discerning reality from stereotypical behavior), who exaggerate role of corporates in giving meaning to a professional's career. The premises of first attack in turn clears way for a second wave of attacks by the same group that now shifts its focus on expectations of corporates in terms of 'loyalty' and links the 'reward or progress' to the actual contribution of employees (although the fact is that these 'logical' explanations are more often than not an outcome of our ingrained tendency to rationalize & explain all events in retrospect). So now the second thing that you need to ask yourself is whether you really want to stay in this environment or you want to create your own thing - i.e. a new business. The option is not too easy to opt for as around 95% of startups packup within first 5 years of inception...
3. Lastly, organizations are nothing but extensions of society. The issues faced by them are similar in nature the issues faced by the wider sections of socities that they are composed up of and moreover these will surface in by an large same proportion. So if a false allegation has been levelled against you then it is not unexpected. If there was an unholy alliance between one of your employees and vendors then again it is not unexpected. It is again not surprising that your boss chose not to act responsibily or not to discourage your resignation as an impulsive reaction to this episode. But again just knowing that the events were not unexpected will not serve any purpose until you come up with an approach on how to immunize or at least make yourself less vulnerable to these or to other such attacks. Whatever you do, wherever you perform, these roadblocks will always be there to welcome you. You need to be smart enough to smash them. In a long career, driven by ethical conduct & a deep sense of responsibility, you will always face some victories and some defeats. What matters is not ti lose your humility when you succeed and never to lose courge when you fail