Long abstract for technical report orphaning Abstract title due to vfil

Question

When using a custom template to prepare a report I noticed that long abstracts split across pages, fine, but it leaves the abstract title hanging by itself on it's own page.

How can I structure the abstract environment to have vertically centered abstracts if they fit on one page and top aligned in long abstracts? The \vfil is useful for centering short abstracts, but then means it orphans the title in long abstracts

Actual Behavior of long abstracts

The intended behaviour of long abstracts

But without breaking short abstracts

The MWE of abstract environment and usage

Normally the environment def is split into the template class.

\documentclass[11pt]{book}
\usepackage{lipsum}

\newenvironment{abstract}
{
  \thispagestyle{empty}
  \null\vfil %Toggling this line will align to the top in multipage abstract
  \begin{center}
    \setlength{\parskip}{0pt}
    {\textsc\normalsize University \par}
    \bigskip
    {\underline{Abstract} \par}
    \bigskip
    {\textsc\normalsize Faculty \par}
    {\textsc\normalsize Department \par}
    \bigskip
    {\normalsize \underline{A progress report submitted for continuation towards a PhD}\par}
    \bigskip
    {\normalsize\bf \title \par}
    \medskip
    {\normalsize by [Author] \par}
    \bigskip
  \end{center}
}
{
  \vfil\vfil\vfil\null
  \cleardoublepage
}

\title{\bf An MWE}
\author{for SO}
\date{\today}

\begin{document}
\frontmatter
\maketitle
\begin{abstract}
\lipsum[1-4]
\end{abstract}
\end{document}

Answer 1

I have found a simple approach without making many changes to your source code. By replacing the center environment \begin{center} ... \end{center} with the switch command \centering inside \begingroup ... \endgroup or between braces with \par gives the desired output.

\begingroup 
  \centering
   ...
\endgroup

or analogously

{\centering
  ...
  \par
}

The intended behaviour of long abstracts

But without breaking short abstracts

MWE (with \begingroup ... \endgroup):

\documentclass[11pt]{book}
\usepackage{lipsum}

\newenvironment{abstract}
{
  \thispagestyle{empty}
  \null\vfil\vfil
    \begingroup
        \centering
        \setlength{\parskip}{0pt}
        {\textsc\normalsize University \par}
        \bigskip
        {\underline{Abstract} \par}
        \bigskip
        {\textsc\normalsize Faculty \par}
        {\textsc\normalsize Department \par}
        \bigskip
        {\normalsize \underline{A progress report submitted for continuation towards a PhD}\par}
        \bigskip
        {\normalsize\bf \title \par}
        \medskip
        {\normalsize by [Author] \par}
        \bigskip
    \endgroup
}
{ 
    \vfil\vfil\null
    \cleardoublepage
}

\title{\bf An MWE}
\author{for SO}
\date{\today}

\begin{document}
\frontmatter
\maketitle
\begin{abstract}
\lipsum[1-2]
%\lipsum[1-6]
\end{abstract}
\end{document}