I believe Sir Thomas will do what he can to ensure Fanny is well settled. I agree he is too responsible to do otherwise but he does want to do right from principle as well as for pride, he has “a desire of seeing all that were connected with him in situations of respectability” (1). If an offer of marriage never appears for Fanny I think it is most likely she would remain at MP with Lady Bertram. A less likely scenario is residing with one of her cousins after they marry. If she returned permanently to her father’s house her status would sink. I am not sure the daughter of a lieutenant of the marines is considered a gentlewoman. If she was forced to earn her own way in the world as a paid companion she would also loose her hard won status—I really don’t think Sir Thomas would throw Fanny off in this way.
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If Fanny receives an offer of marriage I can envision Sir Thomas settling a small dowry on her but he has other methods at his disposal. He could assist Fanny’s intended in his profession as he did by giving Mr. Norris the living of Mansfield. Sir Thomas could not help Lt. Price in his profession but sought to “devise… [an]other method of assisting them” (1). When the breach is finally healed Sir Thomas assists by liberating Mrs. Price from her children one by one. First her eldest daughter and then “he assisted her liberally in the education and disposal of her sons as they became old enough for a determinate pursuit” (2). The narrator says Sir Thomas helped liberally which I take to mean he was very generous—he probably helped William go to sea.
Sir Thomas does not forget his responsibilities which is why I believe he will provide for Fanny whatever her future holds. (:D)