What to do if Fiance visa is not approved??

[Terpe]

They said that it is a strong application and it would be difficult for the ECO to reject it.....

It's true that the ECO will judge the application as a whole, and generally not refuse on just one marginal area.
But the financial test is a key factor and your application in regard to that is highly marginal.

...I thought there was a set amount of weeks at a certain amount of money you had to have etc which I could compare it with so I would know for certain "YES" I do meet the maintenance requirement...

In principle if it is more likely than not that the total amount of money that the applicant and sponsor will have to live on will be below what the income support level would be for a British family of that size, then it may be appropriate to refuse the application on maintenance and accommodation grounds.
Technically the ECO will look to see that you can cover your living expenses without recourse to public funds in the UK for 27 months, if you are applying from outside the UK (24 months from within the UK).
That's more than the 81 weeks indicated in the letter.

...

If it is rejected because of the maintenance requirement could I appeal and possibly be successful in arguing that I meet the maintenance requirement?

I very much doubt you would be successful. In fact it is the Immigration Tribunal's (courts) that have concluded it would not be appropriate to have immigrant families existing on resources that were less than the 'Income Support Level' for a British family of the same size.

Sorry yellowcloud, not trying to be negative, hurtful or offensive. Just putting the facts as honestly as I can in answer to your concerns.

I do really hope the ECO looks kindly on the application.