Partial/Implant overdenture case: Ball attachments or switch to locators?

Be very careful the malpositioned implant may bring you into the failure which you did not cause. This is like driving someone else's used car and you might be set up for a fall. Perhaps have a prosthodontist take a look at it if you feel the second implant will cause a case failure. The fact that you are going to use the abutment provided the patient may assume that you agree with the placement and you will be left holding the bag!

Radiographs and photographs would be helpful.

I'm a prosthodontist. It doesn't matter whether they are clix or locators. They will both handle about 15-20 degrees of misalignment. However, that being said, I hate walking into another persons treatment plan. You will probably be retrofitting the RPD and this treatment plan is a long way from ideal. I like the basic idea but I do not like independent abutments. I'm OK with locators, clix or ball abutments for an overdenture but in your situation with a partial denture and retained #19 I would rather see a bar connecting the two implants with a hader clip anteriorly and a locator or bredent attachment off the distal of the bar on the right (#28 or 4-4 area). spread out the clips as much as possible. However, if you have to refit an existing prosthesis you will then be responsible for all the bad stuff that happens in the future. I don't like to buy into someone else's treatment (retrofit an rpd? really? good luck) I never retrofit except for a mandibular overdenture and two implants with stud type attachments.

A bar is a nice solution for angle problems, however in partially edentulous cases sufficient vertical space is unlikely and almost certainly requires a new prosthesis. In fact, your treatment might include a new partial so it can be designed to accommodate whatever attachment you desire. Work closely with a good lab and determine your ridge to prosthesis' surface space before you start buying abutments. Ball types are usually taller than Locators and angle correction abutments are taller still. I'm not really worried about losing an implant, but rapid wear of attachments or breaking through the partial are also definitions of failure.