Case/Tense question

I'm working on Terra Novan, a descendant of English, and I've come into
a problem with the Future.  Word-final l's were lost, so I'll, you'll,
etc. merged with I, you, etc.  I first thought I'd simply replace it
with "gonna", unfortunately, there's a problem with that, too.  I became
/e/, while I gonna became /egEn/ --> /egE~/ --> /ege~/ --> /ege/ --> /e/
(/E~/ and /O~/ were both raised and /&~/ moved backwards to /A~/; also
intervocalic voiced stops were lost).  I think the other persons would
continue to distinguish future from present, but I'd still like to find
an alternative.  What would be reasonable to replace the lost future?
Perhaps re-creating the "gonna" construction by using /gu/ (go), thus
/ese/ = I see, /egu se/ = I will see, or /egwe se/ (/gwe/ = /gu/ + /e/ <
/iN/), but I don't like the idea of simply recreating the current form.
What other kinds of constructions might be used?

Also, I want to create cases from prepositions.  I'm considering:

To -> dative
In -> locative
With -> instrumental
and so on, the details aren't clear yet.

I want an accusative, but I don't know what could lead to it.  What
would be reasonable?

--
"Old linguists never die - they just come to voiceless stops." -
anonymous
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