My opinion? British are defeated by Carthagena garrison commanded by Carlos Des Naux. The same as in OTL, but without Lezo.
The reason is easy: Vernon was an incompetent. He was also defeated in Cuba and Panama without Lezo. His only "victory" in the Jenkins' ear War consist in destroy a poorly-deffended port like Portobello.
But probably the moral of the spanish garrison would have been weaker and after losing the few ships in the bay they would have offered less resistance. The loses of the english were caused more by the spanish artillerymen than by illness (although these were terrible) according to some witnesses.
Yeah, I know, It´s a 2006 thread, but I´ve got to retake it.
WI the british take control of Cartagena forcing a peace in achieving control of Cuba, the Philippines and the coast of New Granada like wikipedia insinuate that could happen. What´s next?
Not even in XVIII century Spain. Blas de Lezo was court martialled, fortunately he died before being sent to prison... It was not until later that people realized that to defeat an army and a navy several times the force he had to defend Cartagena, although led by an incompetent like Vernon, was the task of an hero.