The literature that I've viewed so far suggests that in Plautine Latin, forms like domust for domus est could be found, but not forms like dom'et for domus et.
Terence and the Verb 'To Be' in Latin, by Giuseppe Pezzini (2015), describes -us est → -ust as (in at least some time periods) a special contraction belonging to est, rather than an example of regular sandhi rules:
the uncontracted spellings (dictus est and usus est) would not automatically prompt contracted pronunciation, since final -s would normally only be omitted before a consonant [...] contracted spellings in -ust are attested in manuscripts and inscriptions [...] contracted forms do not appear to be the product of a sandhi phenomenon but independent clitic forms.
Pezzini also mentions -ist from -is est.
The phenomenon is also discussed in "Where Does Latin Sum Come from?", by Martti A. Nyman1. Nyman indicates that just as -ust can be found instead of -us est, there are examples in Plautus of -uss being used in place of -us ess (for Plautus, the second-person singular of esse ended in a geminate ss):
(10) Mil. 574 sed satine oratuss? :: abi 'but have I begged your pardon enough? :: Off with you'
Mil. 825 eho tu sceleste, qui illi subpromuss, eho 'ha, you rascal, you're his under-butler, so see here'
Nyman says that explaining these forms as resulting from loss of intervocalic s prior to contraction of adjacent vowels is "generally rejected" (page 45) and argues that instead, they can be grouped with the cases where word-final singleton s after a short vowel (especially short u) is lost before a consonant (pages 46-48). This is part of a larger argument that Nyman is making that in Plautus the basic second-person and third-person singular forms of the copula are consonant-inital ss and st, from which the vowel-initial forms ess and est are synchronically derived by a rule of prosthesis ((9), page 43).
- Language, Vol. 53, No. 1 (Mar., 1977), pp. 39-60, accessed through JSTOR